468 



PART III. THE CLASSIFICATION OF PLANTS. 



sporangia. In the other Coniferae the microsporophylls, bearing 

 215 sporangia, show more or less distinct differentiation into 

 a stalk bearing a terminal leafj 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, which can be 



FIG. 296. A Microsporophyllary (or staminal) 

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

 crosporophyll with two microsporangia (pollen- 

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

 mag.) ; eexine expanded into two hollow vesicles 

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



FIG. 297. Pinu* sylvestris (x7: after 

 Strashurger). Macrosporophyll b, bear- 

 ing on its upper surface the placenta! 

 scale fr, which bears two ovules s 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 Conifers, leads on to the more complete differen- 

 tiation and specialisation which obtains in the Gnetacea? and in 

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

 phylls. 



The macrosporophi/ll (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- 



