478 



APPENDIX. 



LOWER END OF OOSPORE 



--2 



SUSPENSOR --. 



ROOT-CAP 

 ROOT-APEX 



tissue of the ovule-bearing (or seed-bearing) scale, and which 

 aids in its dispersal by the wind when the ripe cone opens by 

 lengthening its axis and so separating the seed-bearing scales 

 from each other. 



Now, if we compare the structure of the ovule and the 

 mode of fertilisation in the Pine with the life history of the 



Fern, we can see that 

 the tissue we have 

 called the " primary 

 endosperm " in the 

 Pine ovule corre- 

 sponds to the pro- 

 thallus of the Fern, 

 since it produces 

 archegonia essenti- 

 ally similar to those 

 of the Fern. The 

 cell in the nucellus 

 from which the pro- 

 thallus, or " primary 

 endosperm," of the 

 Pine arises therefore 

 corresponds to a 

 COTYLEDONS spore, the nucellus 



itself to a sporan- 

 gium, and the in- 

 tegument to an in- 

 dusium. 



The " female spore " of the Pine, however, is never set free 

 from its spore-case, but germinates inside it ; the prothallus 

 it produces remains enclosed in the spore-case, within which 

 also the embryo is formed; while the whole of these struc- 

 tures remain attached to the Pine plant. This chain of 

 processes leads up to the sharpest distinction between the 

 Grymnosperms and the Vascular Cryptogams, namely, to the 

 production of the seed. 



In order to understand clearly the correspondences and 

 differences between the life histories of the Fern and the 

 Pine, however, we should have to study a Vascular Crypto- 

 gam in which two kinds of spores are produced such a type 

 as Selaginella, for instance. 



SUSPENSOR 



-EMBRYO 



STEM - - 



Pig. 17. Segmentation of Oospore and Development 

 of Embryo of Pine. 



Only half the number of nuceli, cells, and rows of cells, 

 is, of course, shown in the early stages. 



