416 A TEXTBOOK OF GENERAL BOTANY 
ferns or fernlike ancestors. In general appearance the Cycado- 
filicales were so fernlike that their leaves were believed to be 
the fronds of ferns, until seeds resembling those of the cycads 

Cc d 
Fig. 469. Longitudinal section of seed of Zamia 
a, female prothallus with two archegonia inclosed in a nucellus, and this within 
the integument ; b, older stage in which the nucellus has largely disappeared ; 
c, early stage in the development of the embryo (note the long coiled structure, 
suspensor, which pushes the embryo into the prothallus) ; d, mature seed con- 
sisting of embryo surrounded by prothallus and this by the seed coat formed from 
the integument. The seed coat consists of three layers, a thin fleshy inner layer, 
a thick stony layer, and a still thicker fleshy outer layer. (x 14 
were found attached to them. The vascular anatomy was fern- 
like but with very well-marked secondary thickening in the stem. 
Modern cyeads still show fernlike characters. The leaves 
resemble those of ferns and in some cases are rolled up when 

+ 
a — 
