IN THE VEGETABLE KINGDOM. 49 



capable of germinating, the stylospores, in these cases at least, 

 appear rather to be — like the bodies of the same name among 

 fungi — a secondary form of spores.* They seem to occur 

 with greatest frequency in species most allied to the Fungi. 



In many Lichens we find yet another form of organs, which 

 are undoubtedly of a gemmiparous kind ; these are the sore- 

 dia, little pulverulent masses of the green cells termed goni- 

 dia, of which, generally throughout the order, a stratum is 

 interposed between the medullary and the upper cortical 

 layer of the thallus. The beaded filaments formed by these 

 gonidia are probably the only organic pecuUarity which se- 

 parates the order of Lichens from certain tribes of Fungi, for 

 between these two orders we find a great general similarity, 

 both in the parts of fructification, as now noticed, and in the 

 structure and disposition of the tissues. In both we have a 

 primordial structure or substratum of confervoid filaments, 

 kno^^^l as the mycelium of the fungTis, and the hypothallus 

 of the lichen ; in both also we have generally, but by no 

 means universally, a more compact tissue — the hymenium or 

 crust — developed subsequently to the other, and in more 

 immediate connection mth the organs of reproduction. 



No phenomena of the nature of alternation are as yet 

 known to occur among Lichens. 



§ 6. REPRODUCTION IN HEPATIC^ AND MOSSES. 



These orders introduce us to that hidier division of the 

 Cryptogamia, which is characterized by the formation of a 

 leafy axis. Such an axis first appears in the section of the 

 Hepaticse represented by Jungermannia ; it is universal in 

 mosses, and attains its maximum development in ferns, 

 where it is constituted in part of fibrovascular tissue, while 

 it is entirely cellular in the lower forms. 



* Dr. Lindsay in Edin. Plulos. Joum. (July, 1859), p. 124. 



D 



