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 peculiarity 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, 

 known as the mycelium of the fungus, 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 with 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 higher 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. Philos. Journ. (July, 1859), p. 124. 



D 



