VASCULAR CRYPTOGAMS 



13 



exposed to the action of moisture at the time of maturit}*. 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- 

 diace^e and Ophioglossaceae), on which are borne both the antherids and 

 the archegones. In the heterosporous Salviniaceae the male prothallium 

 is reduced to a simple unseptated germinating filament ; and in 

 Marsileaceae it altogether disappears. In Selaginellace^ it takes the form 

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

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

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



II. 



III. 



Fig. I.— I., male catkin of Zaviia (Cycadeae). 

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



stl- 



Fig. 2. — Peltate scsle oi EquisetJim, 

 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 Coniferce and Cycade^ 

 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 



