REPRODUCTIVE ORGANS 
55 
megaspores in megasporangia on megasporophylls. Only 
rarely do both kinds occur on one leaf, e.g. in Marsiliaceae. 
In the ferns proper the sporophylls are not usually 
differentiated from the foliage-leaves ; the same leaf usually 
both assimilates and bears the sporangia. In other Pterido- 
phyta there is a differentiation of the reproductive part of 
the shoot ( inflorescence or strobilus) from the rest, and the 
same is the case in the Spermaphyta. In Equisetum and 
in Lycopodium there is a cone of sporophylls, all of one 
kind in Selaginella the cone consists of micro- and mega- 
sporophylls. The same is the case in the Gymnosperms 
and Angiosperms, stamens and carpels corresponding to 
micro- and mega-sporophylls, polle?i-sacs and ovules to micro- 
and mega-sporangia. 
There is good reason for believing that the structural 
separation of the reproductive and vegetative functions took 
place at least as early as the separation of the vegetative 
functions from one another; hence it is evident that we 
must be careful in comparing the organs of reproduction 
with the vegetative organs. We have no right to say, for 
example, that a sporophyll is a modified vegetative leaf ; 
perhaps we should be nearer the truth if we said that a 
vegetative leaf was a modified sporophyll, for the sporophyte 
was probably reproductive before it was vegetative. It is 
convenient and justifiable to speak of the sporophylls as the 
leaves of the reproductive shoot, as their mode of arrange- 
ment, development, &c., correspond closely with those of 
the leaves of the vegetative shoot, but we must beware of 
assuming that the structural phenomena of the one shoot 
must necessarily have their counterparts in the other. 
The spores of ferns and other Pteridophyta are shed 
upon the ground and there germinate, giving rise to little 
sexual plants, usually green, termed prothalli , entirely 
different in habit and structure from the asexual leafy 
plants. On these the male and female cells or gametes, 
called spermatozoids ( antherozoids ) and ova respectively, are 
borne in receptacles called antheridia and archegonia. The 
prothallus in this connection is called the gametophyte ; in 
homosporous forms (except Equisetum) it usually bears both 
sexes, while in Equisetum and the heterosporous forms there 
are male and female prothalli. 
