INTRODUCTION TO CRYPTOGAMIC BOTANY. 93 



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

 these lower Algas, 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 Palmellw of Seirosiplion, 

 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 

 Collema hulbosum, and a Glceocapsa on that of Cladonio pyxi- 

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

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

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

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

 formation of a gonidium. When the Olceocapsa is once formed 

 it increases rapidly, forming a gelatinous mass, entirely distinct 

 from the Cladonia. 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 Seirosiplion are similarly circumstanced. When we 

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

 genera must eventually be expunged. 



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

 general characteristics of Alga^ ; but, as in Pha^nogams, the 

 parenchymatous cells sometimes contain sj^iral 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 Algas. In Zygnenia, for instance, and its allied 

 genera, we have repeated examples, sometimes exhibiting a 



* Zur Entwickelungsgeschichte des Collema hulbosum, Acli. von Julius 

 Sachs. 



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

 stem of Lichina, and simulating distinct Algfe. 



