S8 



GYMXOSPERMS 



The ovules are prevailingly small, many of them not more than 

 5 mm. in length, and few of them exceeding a centimeter. Just 

 what the structure is and how it compares wuth that of groups above 

 and below has not yet been determined very definitely. The best 

 illustrations available are drawn from later stages in Cycadcoidea 

 darloni and Bcnncitilcs morcri (figs. 52 and 53). The outer layer is 

 thick and palisaded at the top; the middle layer, shown in black in 



Tic;. 53. — Cycadeoidea darloni: longitudinal section of ripe seed with a dicotyl em- 

 bryo; X20. — .'\fter WlELAND.**' 



the figure, is stony, and the thinner inner layer is probably mem- 

 branaceous. The thin line, at a little distance from the embryo, may 

 be the megaspore membrane. The complicated micropylar end of 

 the ovule is a striking feature. 



The embryo. — It will be remembered that in the Cycadofilicales no 

 embryo has yet been found. The almost constant presence of dicotyl 

 embryos in the Bennettitales is in striking contrast. As shown in 

 figs. 51 and 53, the hypocotyl is more extensive than in the living 

 cycads, and the suspensor, if present, could not have been very prom- 

 inent. 



