468 



PART III. — THE CLASSIFICATION OF PLANTS. 



spoi'an^a. In the other Coniferae the microsporophylls, bearing 

 2-15 sporangia, show more or less distinct, differentiation into 

 a stalk bearing a terminal leafy expansion, until, in Taxus, a 

 stage is reached where the microsporophyll consists of a stalk 

 bearing a peltate lamina, on the under surface of which the spor- 

 angia are developed. In other words, the microsporophyll con- 

 sists of a filament bearing a sorus of sporangia which constitutes 

 an anther (see p. 432). In all cases the microsporangia are 

 developed on the morphologically under (dorsal) surface of the 

 sporophyll. 



The gradual differentiation of the microsporophyll, v^hich can be 



Fig. 296.—^ Microspnrophyllary (or staminal) 

 flower of Abies pectinata ; b scaly bracts ; o mi- 

 crosporophyll with two microsporangia (pollen- 

 pacs). B Microspore (pollen-grain) (highly 

 mag.) ; e exine expanded into two hollow vesicles 

 11); y male prothallium. (After Sachs.) 



Fig. 297. — Pmus sylvestris (x7: after 

 Strasburger). Macrosporophyll b, bear- 

 ing on its upper surface the placental 

 scale /)•, which bears two ovules » at its 

 base; c apophysial projection of the 

 placental scale ; m prolonged integument 

 of the ovule within which pollen-grains 

 have lodged. 



traced in the Conifera?, leads on to the more complete differen- 

 tiation and specialisation which obtains in the Gnetaceae and in 

 the Angiosperms. In Gnetum, however, there are no microsporo- 

 phylls. 



The macrosporophyll (carpel) appears in a simple, yet typical, 

 form in Cycas (see Fig. 303), the one Gymnosperm which has no 

 distinct macrosporangiate flower. Here the carpels are essentially 

 similar to the foliage-leaves, though they are smaller, of a yellow 

 colour, and of a somewhat different form : they are, in fact, de- 



