EMBRYO-SAC OF GYMNADENIA CONOPSEA. 
11 
toplasmic substance [can.') which result from the partial 
division of a small piece of the oosphere, which becomes 
early cut off from that body ere it rounds off in the body of 
the archegonium ; these masses are the ‘‘ canal cells of the 
Germans, and by degradation become mucilaginous, and so 
serve to fix the antherozoids. 
Fig. 1. — Diagram of free protb allium of fern, with its archegonium pro- 
jecting some distance exteriorly, and possessing a many-celled neck 
in the canal of which are the “ canal cells.” 
Although the spores of Ferns present no external charac- 
teristics from which we can infer whether the prothallia to 
be produced on germination will be predominantly male or 
female, u e. in its whole course of existence will bear arche- 
gonia or antheridia in excess, still we may see here indica- 
tions of a differentiation of function which, attended hy 
reduction and abbreviation of tbe prothallus and processes 
peculiar to it, attains a limit in the highest plants. If in 
this specialisation and distribution we see an economy of 
material and energy, we can at the same time explain many 
of the phenomena. 
In the Rhizocarps the separation of the sexes has been 
carried so far that from the spore itself we can predict 
whether archegonia or antheridia will be formed on its ger- 
mination, in some cases even the sporangia participating in 
the separation, and being distributed on different parts 
according as their products will yield male (microspore) or 
female (macrospore) prothallia. The male or antheridium- 
bearing prothallia are very small, becoming reduced to a 
mere tube of two or three cells in Salvinia, and in others 
being only represented by the trace of protoplasm left over 
from the antherozoid mother-cells. We must, in fact, look 
upon certain cell divisions in the microspore, preceding its 
germination, as representing the formation of a rudimentary 
prothallus and antheridia which form the few' antherozoids 
then liberated. 
In the niacrospore, though the prothallus is also not set 
free, it is more obviously a cellular structure, producing one 
