GYMNOSPERM^. 



119 



then incised and segmented, and lastly pinnate ; in which cases they would have once 

 presented a remarkable affinity with certain abnormal Corddites and Salisburiea. The 

 analogy is increased by the presence, common to all these, of a peculiar cellular tissue, 

 called " tissu lacunaire" in the middle of the substance of the leaf and uniting the veins. 



The flowers of the Cycadacete are always dioecious, the plants being either male or 

 female. They are placed at the summit of the stem, and in all the genera except Cycas, 

 they externally resemble fir-cones. The female flower of Cycas is composed of a 

 whorl of metamorphosed foHage-leaves, several of the lower pinnae of which support 

 ovules. These attain a considerable size even before fertilisation, and the fertilised 

 seed " acquires the dimensions and the appearance of a moderate-sized ripe apple, 

 hanging quite naked on the carpel."' The stem continues to grow through the whorl 

 of modified leaves forming the female flower, developing first a whorl of scale-leaves 

 and then new whorls of foliage-leaves. Saporta and Marion point out that this is the 

 utmost simplification of which phanerogamous plants are capable, and indicates very 

 clearly the stages through which their evolution from Cryptogams must have progressed. 

 The male flower is composed of numerous smaller undivided staminal leaves, expanded 

 from a narrow base and crowded on the under side with pollen-sacs. In other Cycads 

 the staminal or carpellary leaves are disposed on a shorter and relatively slender stem, 

 and become often hard or lignified. The pollen-cells or microsporangia are grouped in 

 clusters of three or five on the under side of the staminal leaves, like the sori on Ferns. 

 They open longitudinally, and, according to Sachs, " are in all respects much more like the 

 sporangia of Ferns than the pollen-sacs of other Phanerogams, from which they also differ 

 in the firmness and hardness of their wall."^ The relative size of the grains, their often 

 elliptical form and median furrows are, on the other hand, special to Cycads. The grains 

 are at first formed of only one cell, but subsequently this divides into two cells, the larger 

 of which becomes fashioned into the pollen-tube whilst the smaller again subdivides, so 

 that a Cycadean pollen grain is normally three-celled ; a character helping to assimilate 

 the Cycads with ordinary Gymnosperms. The carpellary leaves are crowded in a spiral 

 arrangement on the axis of the female flower, except as just described in Cycas, each one 

 bearing two ovules on the under surface of the peltate or expanded lamina. Saporta and 

 Marion regard it as probable that they were originally more numerous, covering the 

 surface of the limb, and that the reduction in number is an advance in their evolution. 

 In Corddites the fruiting organ is a shoot with greatly modified leaves, the main 

 axis bearing only sterile bracts, from the axils of which the staminal or carpellary 

 leaves are developed, while the bracts serve as involucres. In Ginlcyo the male flower 

 consists of an axis with staminal leaves bearing pollen-sacs at their summits, much as in 

 Corddites ; but in the female flower there is no axis, and it consists only of isolated 

 carpellary leaves springing from the axils of foliage leaves, and bearing two, or rarely three, 

 ovules at its extremity. 



1 Sachs, p. 503, English Edition, 1882. 3 L. c, p. 504. 



