INTRODUCTION TO CRYPTOGAMIC BOTANY. 93 



course of his investigations, was led to suspect that many of 

 these lower Algse, however beautiful and interesting as micro- 

 scopical objects, were not autonomous ; many seemed to pass 

 into each other by intermediate forms, and others were so con- 

 stantly the attendants of others, as Palmellce of Seirosiphon, 

 that he was led strongly to suspect some very close and inti- 

 mate connexion ; and this is formally enunciated in a late 

 number of the Botanische Zeitung, Jan. 5, 1855.* M. Sachs 

 professes to have seen a Nostoc generated on- the surface of 

 Gollema bulbosum, and a Glwocapsa on that of Cladonia pyxi- 

 data.-f It is to be observed, however, that he is not sure 

 whether the Nostoc has arisen from the spores of the Gollema, 

 or from its gonidia, but he speaks positively as to the origin 

 of a Glwocapsa from the threads of the lichen by the trans- 

 formation of a gonidium. When the Glwocapsa is once formed 

 it increases rapidly, forming a gelatinous mass, entirely distinct 

 from the Gladonia. Supposing this to be true, it is not a 

 transformation of a lichen into an Alga, but the supposed Alga 

 is a mere condition of the lichen ; and if all species of the 

 genus belong to the same category, the genus must be erased 

 from the system, as has been the fate of many genera once sup- 

 posed to be autonomous. There is great probability in favour of 

 such a supposition, and it will perhaps be found that most 

 species of Seirosiphon are similarly circumstanced. When we 

 come to the consideration of fungi, we shaU find how many 

 genera must eventually be expunged. 



72. The total absence of vascular tissue is one of the most 

 general characteristics of Algae ; but, as in PhEenogams, the 

 parenchymatous cells sometimes contain spiral threads, as, for 

 instance, in the aerial roots of Orchids, or the little bulb- 

 shaped processes which are are so common on the roots of 

 Conifers ; so also there are undoubted instances of spiral 

 threads in Algee. In Zygnema, for instance, and its alhed 

 genera, we have repeated examples, sometimes exhibitmg a 



* Zur Entwickelungsgeschichte des CoUemabulbosum, Ach.vonJulmB 



Sachs. 



t Mr. Thwaites found discs of cells regularly pullulating from the 

 stem of Lichina, and simulating distinct Algse. 



