GROUP V. ANGIOSPERM^:. 459 



from the claws (Fig. 275 B l\ Any segmentation of the petal, as 

 in the Pink (Fig. 275 A) is unusual ; emarginate or obcordate 

 petals are more common. In many cases the petals have spur- 

 shaped appendages (Violet, p. 455), or they are prolonged at the 

 base into tubes, as in Helleborus and Aconitum. This peculiarity 

 is connected with the secretion of the nectar 



The Reproductive Organs of the Flower are sporangia of two 

 kinds, microsporangia and macrosporangia, borne usually on 

 sporophylls, though sometimes directly on the floral axis. The 

 flower is usually monoclinous ( $ , hermaphrodite, see p. 395) ; but 

 it is not infrequently unisexual, in which case the flowers are 

 either microsporangia te ( , staminalj or macrosporangiate ( ? , car- 

 pellary). The plants which have unisexual flowers may be either 



P , 



FIG. 275. A Petal of Dianthus superbus, with (n) the claw and (p) the limb, much divided. 

 B Petal of Lychnis : n claw ; p limb ; I ligula. C Flower of Potentilla, seen from below : 

 c corolla; fc calyx ; a epicalyx. 



moncecious (e.g. Zostera, Arum, Carex, Typhaceae, Zea, Betnlaceae, 

 Euphorbia, Buxus, Juglans, Quercus, etc.) : or dioecious (e.g. some 

 Palms, Vallisneria, Cannabinacese, Salicacese, Mercurialis, Yiscum, 

 etc.) : or polygamous. Of polygamy there are several varieties : 

 thus, the plant may bear monoclinous flowers and staminate 

 flowers (e.g. Veratrum, ^Esculus Hippocastanum, Celtis) ; or mo- 

 noclinous flowers and carpellary flowers (e.g. Thymus vulgar is and 

 T. Serpyllum, Parietaria dijfusa and P. officinalis) : or it bears 

 monoclinous flowers and both staminate and carpellary flowers (e.g. 

 Fraxinus excelsior, Saponaria ocymoidcs}. 



Some flowers are probably primarily unisexual ; that is, there 

 is no reason to believe that the unisexual condition is due to 

 the suppression of either micro- or macrosporangia (e.g. Hemp, 

 Oak, Walnut, Poplar, Willow). Others are secondarily unisexual : 

 that is, there is reason to believe, either from their development 



