POTATO-FUNGUS. 

 Fig. 5. 



109 



1 and 2. Peronospora Alsinearim, Caspary, on Siellaria media, Smith. 

 0. Oogonia. n. Antheridia shortly after fertilisation. A considerable portion of 

 the mycelium is shown in Fig. 2. 



3. Peronospora grisea, Unger. pogonium and oospore not quite mature, 

 median (optical) section. AU magnified aboat 390 diam. 



while at the same time there is formed on its outer surface, from the 

 peripheral or surrounding protoplasm, the oater membrane (epispo- 

 rium), which is mostly of a very dull colour, often dark. The oospore 

 grows in this way from the globule in the oogonium. The walls of 

 the oogonium and the antheridium may either assist the mature 

 oospore or wither. 



The mode of germination of the ripe oospore is known in Cystopus 

 candidus, and in some species of the Peronospores pleuroUastes {P. 

 FalerianellcB, P. Ahinearum). In Cystopus the oospore produces nume- 

 rous zoospores ; and as regards the formation and further development 

 of these all that has been already said respecting zoospores holds good. 

 In the species of Perotiospora just mentioned, each germinating oospore 

 sends out a mycelium tube, like that of the conidium belonging to it. 

 It is, therefore, quite probable that the species of Peronospora which, 

 like Cystopus, produce zoospores from their conidia, present also the 

 same phenomenon in connection with the oospores. 



Up to this time the sexual organs have not been observed in Phyto- 

 'phtJiora, the Potato-fungus. What is known of it in other respects 

 corresponds so well with Peronospora that there is doubtless every 

 reason to expect exactly the same sexual organs in the one as in 

 the other. Still this is not certain ; and, in particular, stress must be 

 laid on the fact there is another group of Fungi to which, as far as our 

 knowledge goes, the Potato-fungus might with equal reason be com- 

 pared ; I refer to the family of Saproleyniece, Fungi which for the most 



