VASCULAR CRYPTOGAMS 



J3 



exposed to the action of moisture at the time of maturity. Hence, in 

 all the isosporous Vascular Cryptogams, by far the largest portion of the 

 product of germination of the hermaphrodite spore is the cellular tissue 

 or prothallium (reduced to a comparatively small size in the Lycopo- 

 diaceae and Ophioglossacese), on which are borne both the antherids and 

 the archegones. In the heterosporous Salviniacese the male prothallium 

 is reduced to a simple unseptated germinating filament ; and in 

 Marsileacese it altogether disappears. In Selaginellacese it takes the form 

 of the small sterile cells at one extremity of the microspore ; ih Gymno- 

 sperms, of the sterile cells of the pollen-grain ; in Angiosperms it is 

 almost entirely suppressed. The contents of the pollen-grain corre- 



FlG. I.— I., male catkin of Zamia (Cycadeae). 

 II. III., antheriferous scale and pollen-sacs. 



FlG.^ 2. — Peltate scale of Eguisehtm^ 

 with sporanges sg, (After Sachs.) 



sponding to the antherozoids, the pollen-grain itself becomes homologous 

 with the microspore, the pollen-sac or anther-cell to the microsporange. 

 Even in external appearance the pollen-sacs of Coniferse and Cycadeae 

 bear a striking resemblance to the sporanges of some Vascular Crypto- 

 gams. The modes of formation of the pollen-grains within the pollen- 

 sac and of spores within the sporange, from an original archespore, are 

 identical in their main features. 



Turning now to the female organs of reproduction, we must trace 

 the homology of these back from the product of the union of the two 

 elements, which in all the higher plants, whether flowering or flowerless, 

 may be termed the oosperm, developing later into the embryo. In 



