THE SPOEE AND ITS DISSEMINATION. 129 



form of the spores and their size differ materially, as well as the 

 manner in which they are produced on the threads. In many 

 they are very minute and profuse, but larger and less plentiful 

 in the Dematiei than in the Mucedim.es. The »pores of some 

 species of Helminthosporium are large and multiseptate, calling 

 to mind the spores of the Melanconiei. Others are very curious, 

 being stellate in Triposporium, circinate in Helicoma and Helico- 

 coryne, angular in Gonatosporium, and ciliate in Menispora cili- 

 ata. Some are produced singly and some in chains, and in some 

 the threads are nearly obsolete. In Peronospora, it has been 

 demonstrated that certain species produce minute zoospores 

 from the so-called spores. The dissemination of the minute 

 spores of the Mueedines through the air is undoubted; rain also 

 certainly assists not only in the dispersion of the spores in 

 this as in other groups, but also in the production of zoospores 

 which require moisture for that purpose. The form of the 

 threads, and the mode of attachment 

 of the spores, is far more variable 

 amongst the Mueedines than the form 

 of the spores, but the la*tter are in all 

 instances so slightly attached to their 

 supports as to be dissevered by the 

 least motion. This aids also in the 

 diffusion of. the spores through the 

 atmosphere. 



Sporangia are produced in the 



t.7 . . -,, ,, , • Fig. 63. — Spores of Helicacoryjie. 



Physotnycetes usually on the tips or 



branches of delicate threads, and these when mature dehisce and 

 set free the minute sporidia. These are so small and uniform 

 in their character that they require but a passing mention. 

 The method of diffusion agrees much with that of the Mueedines, 

 the walls of the sporangia being usually so thin and delicate 

 as to be easily ruptured." Other modes of fructification prevail in 

 some species by the production of cysts, which are the result of 

 conjugation of the threads. These bodies are for the most part 

 furnished with thicker and more resistant walls, and the diffusion 

 of their contents will be regulated by other circumstances than 



