Sectioned and intact shoot apices from Potentilla fruticosa L. plants producing singe and double flowers were examined using optical and scanning electron microscopy. In both flower types the whorls of floral organs were initiated in a helical pattern similar to that of the foliage leaves, although the interval between successive primordia was decreased. The petals and stamens were initiated on a pentagonal ridge surrounding the apex. A primordium was initiated at each vertex of this ridge and about five others along each side. Initially there were no apparent differences among these primordia. The primordia at the vertices always developed into petals. In single flowers all other primordia on the ridge developed into stamens. In double flowers the primordia adjacent to those at the vertices developed petalloid characteristics in the same sequence in which they were initiated. The extra petals are thus found in positions otherwise occupied by stamens, and form at the expense of stamens. Quantitative analysis of petal and stamen numbers support this conclusion.

Potentilla fruticosa is a dwarf north temperate circumpolar species. Numerical and experimental taxonomic approaches were utilized to study the taxonomy of this species. The Gower general coefficient of similarity was calculated for 127 representatives, including wild material from North America, Europe, and Asia, as well as cultivars. Interpretation of cluster analysis suggests that all accessions are variants of a common central theme (over 80% similarity). Hybridization may have clouded any distinct phenetic differences. Eight geographic representatives were selected to study breeding relationships. All were successfully crossed with the exception of a tetraploid plant. Heteroploid matings were noted by a reduced success rate. Backcrosses to existing putative F1 hybrids were successful. On the basis of this study, P. fruticosa should be used as the species name for the shrubby cinquefoil complex.

Twenty-four morphological characters of native Manitoba Populus were studied in an attempt to delineate species and variants and provide keys for correct identification. The results support the hypothesis that the variants have originated from intersectional hybridization of P. balsamifera L. (section Tacamahaca Spach.) and P. deltoides Marsh. var. occidentalis Rydb. (section Aegeiros Duby). Populus × jackii Sarg. encompasses the collective group of individuals resulting from this hybrid cross. The hybrid individuals are widely distributed and occur commonly where the two parental species are growing together.

RONALD, W. G., L. M. LENZ, and W. A. C U M~I I N G .1973. Biosystematics of the genus Popllllls L. 11. Chemotaxonomy, phenology, fertility, and segregates of native Manitoba species and variants. Can. J. Bot. 51: 2443-2450. Chemotaxonomical, phenological, fertility, and hybrid segregation characteristics have further el~~cidated the relationships of Poplllrls species and variants in southern Manitoba.S ecies chromatograms, made with bark collections from widely separated localities, were consistently unigrm and proved reliable for species identification. Chromatograms of variant individuals were unlike those of any species examined. Flowering and seed shedding in P. balsai71ifera L., P. delloides Marsh. var. occiderzrnlis Rydb., and variants occurred together and about 2 weeks and 4 weeks later than respective dates for P. rrei7111loicles Michx.Hybrid fertility, measured by seed set was lower than the expected values for fully fertile hybrids of P. bnlsan~ifera and P. rleltoi(1es var. occider~trrlis. All variant pop~~lations, except from Grand Beach, produced greater than 90% vigorous seedlings. Seedling progenies from several apparent F1 hybrids segregated towards P. bnlsanl~era and P. deltoides var. occide~~mlis. No segregates similar to or approaching P. trenillloides were recovered. RONALD, W. G., L. M. LENZ et W. A. CUMMING. 1973. Biosystematics of the genus Poprrllls L. 11. Chemotaxonomy, phenology, fertility, and segregates of native Manitoba species and variants. Can. J. Bot. 51: 2443-2450. Des caracteristiques ayant trait k la chimiotaxonomie, b la pht~~ologie, h la fertilite et B la segregation des caractkres chez les hybrides ont clarifiC les relations entre les espkces et les variantes de Poprrllls dans le sud de Manitoba. Les chromatogrammes, effectuts h partir de collections d'kcorces provenant de localites trks eloignees les unes des autres, Ctaient toujours uniformes pour une espece donnee et se sont donc rCvelCs comme des caractkres scrs pour l'identification des espkces. Les chromatogrammes obtenus de variantes n'etaient semblables B aucun de ceux des espkces itudiies. La floraison et la Liberation des graines chez P. balsnmifera L., P. rleltoides Marsh. var. occidetztalis Rydb. et les variantes se produisent au m&me moment, mals environ deux et quatre semaines plus tard, respectivement, que chez P. tret~ltloides Michz.La fertiliti des Ilybrides, mesurCe par le nombre de graines, avalt une valeur plus basse que les valeurs attendues pour les hybrides complktement fertiles entre P. balsan~ifercl et P. deltoides var. occidetztalis. Toutes les populations de variantes, sauf celles provenant de Grand Beach, ont produit plus de 907, de plantules robustes. Les plantules provenant des graines de plusieurs plantes apparemment hybrides de FI ont montri une segregation en direction de P. babun~ifera et de P. rlelroides var. occidetztnlis. Aucun sigrigat semblable au P. treinllloides ou s'en approchant n'a Cte rencontri.[Traduit par le journal]

The self-incompatibility system in Potentilla fruticosa was investigated by examining pollen cytology, and by analysing intercrosses between two self-incompatible, cross-compatible cultivars of the species. The pollen was found to be binucleate, which is consistent with a single locus self-incompatibility system acting gametophytically in the pollen. This was confirmed by the results of the intercrosses. A proposed model for the inheritance of extra petals was tested by backcrossing selected F1 hybrid plants to both of their parents. Non-random segregation of the double modifier (Dm) locus suggested linkage to the self-incompatibility locus (S). The model was accordingly modified to include this linkage.