422 



PART IV. CLASSIFICATION. 



(Taxeae, Cycas, Gnetaceae) they have various and specialised 

 forms. 



The microsporopliyll (stamen) occurs in its simplest form in the 

 Cycadaceae, where it is a large stout scale bearing usually an in- 

 definite number of microsporangia on its under surface. In some 

 of the Coniferae (e.g. Pinus), the microsporophyll essentially re- 

 sembles that of the Cycadaceae, though it is much smaller (in 

 proportion with the smaller flowers) and bears only two micro- 

 sporangia. In the other Coniferse 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 



FIG. 217 . A Microsporophyllary (or staminal) 

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

 crosporophyll with two microsporangia (pollen- 

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

 inag.) ; e exine expanded into two hollow vesicles 

 II) ; y male prothallinm. (After Sachs.) 



TIG. 248.-Pinus sylvesl ris ( x 7 : after 

 Strasburger) : Macrosporophyll b, bear- 

 ing on its upper surface the placental 

 scale /r, which bears two ovules at its 

 base; c apophysial projection of the 

 placental scale; m micropyle of the 

 ovule within which pollen-grains have 

 lodged. 



bearing a peltate lamina, on the tinder 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 anthei- (see p. 395). 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 

 traced in the Coniferae, leads on to the more complete differen- 

 tiation and specialisation which obtains in the Gnetaceae and in 



