Ever since the classical period of botany it has been widely recognized that the correct interpretation of the morphology of inflorescences presents a most difficult problem. This is because of the immense diversity of forms exhibited by inflorescences of angiosperms and on these their differences in habit largely depend. Since differences in the arrangement of flowers are characteristic of smaller or larger taxonomic groups of angiosperms, it is usual to include these characters, as well as other features, in the diagnosis of a plant. But this is usually done in a descriptive manner only, especially by studying and describing the mode of ramification and foliation within the flowerbearing parts of the plant. For this purpose a very elaborate descriptive terminology is generally adopted, characterizing flower systems as dichasia, racemes, spikes, umbels, panicles, capitula etc. A recent survey of this terminology and its history has been given by Rickett (1944Rickett ( , 1955.I n phytography this terminology is adequate, for here it is necessary only to give a clear portrayal of a plant, so that it will be possible to recognize it and to distinguish it from its relatives. For comparative purposes, on the other hand, such as those involved in systematics, a descriptive classification of inflorescences turns out to be insufficient. While systematics must be based on a comparison of homologous structures, it does not follow that flower-bearing parts to which a single descriptive term is a t present applied are necessarily homologous. For example the inflorescences of Onagra biennis and Plantago m j o r respectively may be termed spikes, but their morphology is, * Sea footnote on p. 220. t The term 'paracladium' is more comprehensive than the term 'enriching branch', since it refers not only to flower-bearing branches but elso includes those branches which either never produce flowers or do 80 under rare and specific conditions. Thus within the whole branching system even the innovation shoots have to be regarded as paracladia of a s p i e l type. By taking the whole branching system of a plant into consideration i n this way, and this is essential if homologiea are to be correctly interpreted, we ikd that there is an essential Werance between Troll's conception and previous attempts to elucidate the structural laws of inllorescences.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. International Association for Plant Taxonomy (IAPT) is collaborating with JSTOR to digitize, preserve and extend access to Taxon. SummaryThe inflorescences of Magnoliales exhibit a wide range of diverse forms. Monotelic inflorescences prevail by far. Panicles or thyrses terminating the flowering shoots are relatively rare, mostly the main axis shows a proliferating growth, then bearing "axillary" inflorescences only. By reduction of the ramification of the flower bearing axis, botryoids or even further reduced inflorescences can be formed. Solitary flowers terminating leafy shoots are also found in several families of the Magnoliales (as well as in Dilleniales). Highly specialized long shoot-short shoot systems are not rare (Calycanthaceae, Schisandraceae, Winteraceae, Eupteleaceae, Tetracentraceae, Cercidiphyllaceae, Eucommiaceae, Myristicaceae), and even cauliflory occurs. Progression to an inflorescence of the polytelic type is relatively rare and occurs especially in some genera of the Lauraceae and apparently generally in Hernandiaceae and probably in members of Myristicaceae.The question, how inflorescences may have evolved and what might be or might have been the primitive form of an inflorescence has been answered in different ways. Since we have been dealing with the morphology of inflorescences in angiosperms for many years we were often asked this question (Weberling, 1982(Weberling, , 1983a) and thus we may discuss it here with special reference to the so-called primitive angiosperms. In our terminology we follow Troll (1964/1969), Troll and Weber (1957), and Weberling (1982, 1983b).Leaving aside the old assumption of de Candolle (1827), that flowers are axillary branches, we find mainly two different opinions, which were expressed by Parkin (1914) and Pilger (1921). The suggestions of Parkin can be traced back to St. Hilaire (1840, p. 276). We may quote them from his summary (Parkin, 1914, pp. 559-560) without going too far into details: "From a comparative study it seems highly probable that flowers were originally borne on the plant singly, each terminal to a leafy shoot ...." "From such a shoot (or shoots) ... all inflorescences, as well as the solitary axillary flower have probably arisen." "The first flower-cluster ... is formed by two or more axils below the terminal flower pushing out lateral floral shoots." Looking for evidence to confirm his assumption Parkin (1914, p. 521) asked: "Do plants still exist exhibiting this early mode of flower-bearing?" and then stated, that "the most conspicuous examples of solitary terminal flowers occur in those families-e.g., the Magnoliaceae, Ranunculaceae, etc.-which on other grounds are now generally regarded as primitive...

Great diversity is found in inflorescences of angiosperms. According to Troll this is due to the variation of two types only: the polytelic and the monotelic type. In the monotelic inflorescence, the apex of the inflorescence axis commonly ends with a terminal flower. This also applies to all the floral branches below the terminal flower. All of these branches, whether branched or not, proved to be homologous elements, and they are all referred to by the term ‘paracladia’ because these branches repeat the structure of the main axis of the flowering system. Accordingly, their ramifications are called paracladia of the 2nd to nth order. Since by the presence of the paracladia the number of flowers in the flowering system is increased, they may be called ‘enriching branches’. Consequently the whole area which produces the enriching branches may be designated as an ‘enriching field’. In the lower part of the flowering shoot this zone is commonly preceded by a ‘field of inhibition’ within which the development of paracladia is inhibited more or less abruptly. The same zonation can be recognized in the individual paracladia if these are not reduced in any way. In perennials, the axillary buds at the base of the whole stem do not develop within the same season, but will give rise to the innovation shoots at the beginning of the following season. Therefore this area has to be distinguished as a ‘field of innovation’. The polytelic type of inflorescence probably has been derived repeatedly from the monotelic during the evolution of angiosperms by reduction of the terminal flower and specialization of the paracladia of the monotelic system. The distal elements are reduced to single lateral flowers or lateral cymes (partial florescences) which constitute elements of an apical system composed of lateral flowers. Instead of ending in a single flower, the floral axis thus terminates in a multi-flowered so-called polytelic ‘florescence’. The lower lateral branches repeat the structure of the main stem by producing (indefinite) florescences themselves and therefore may be termedparacladia (of the polytelic system). As in monotelic inflorescences the area of paracladia — the ‘enriching field’ — can be preceded by a ‘field of inhibition’ and, in perennial plants, by a ‘field of innovation’.Though generally we may confirm that the inflorescences of all species investigated (about 20 000 from nearly all angiosperm families) proved to be variations of one of the two fundamental types, it sometimes needs morphological experience to apply Troll’s system to woody plants of tropical regions. Difficulties may derive from prolepsis and syllepsis of the innovation shoots, prolification of the inflorescence axis and, abundantly, by the deficiency of clearly marked limits between sprouts growing in different seasons. In each of such cases, however, the homologous flower-bearing-elements can be identified by comparing their positions within the whole system of ramification.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. International Association for Plant Taxonomy (IAPT)is collaborating with JSTOR to digitize, preserve and extend access to Taxon.