Received i 2.iii.591. PSEUDOGAMY IN APOMICTIC RUBUS THE polyploid species of Rubus which comprise most of the European blackberry population are apomictic, in contrast to the few diploid species, such as the two primary European species R. u1mfolius and R.tomentosus. It is essential for fruit setting in these pseudogamous apomicts that they must be pollinated with viable pollen (Darrow and Waldo, 1933;Crane and Thomas, 1940; Gustafsson, i943).Focke used the term pseudogamy in i 88i for "parthenogenetic development where pollen-tubes effect the embryo-formation without any previous fusion of egg and sperm nucleus" (Gustafsson's translation), and it will be used in this sense in this paper. In his review of pseudogamy in apomictic Rubus species, Gustafsson (I93) has stated that " pseudogamy" consists of an act of "partial fertilisation ", that is fertilisation of the endosperm nucleus but not of the eggs, and is not due solely to hormone activity. That the latter part of this statement is probably correct is supported by the failure in the present study to obtain stimulation in R. laciniatus after brushing the ripe stigmas with freshly prepared concentrated aqueous extract of its pollen. Pollen from the related genus Rosa is ineffectual. Those pollinations of pseudogamous facultative apomicts which result in more or less maternal-like seedlings, and with the production of only an occasional sexual hybrid when the pollen from another species is used, are given in inverted commas in this paper. A proposed life-cycle for the apomictic tetraploid species R. laciniatus is given in fig. i, and is based on the cytological observations of Kerr This cycle is concerned only with the production of the tetraploid apomictic seedlings. The chief difference between sexual and pseudogamous Rubus species lies in the establishment of the megagametophyte, usually only one gametophyte develops in the sexual whereas from two to four are formed in the pseudogamous species, but the supranumerary gametophytes disintegrate as development progresses.The relative frequency of diplospory and apospory is a specific characteristic, according to Christen (1950).Two series of investigations have been made in an attempt to explore further the genetical and evolutionary properties of pseudogamy in Rubus. The first study was initiated to determine whether

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