On the Resting -Spores of certain Fungi. 37 



Spermatozoids, a similar condition may obtain in these 

 antheridia. The provision made for the rapid development of 

 these parasites and for the preservation of species is truly 

 marvellous, and sufficiently accounts for the difficulty of exter- 

 mination, and their apparently sudden dispersion, especially in 

 wet weather. Besides, wherever any portion of an infected plant 

 outlives the winter, there is a stock of mycelium, ready to 

 throw out fresh fertile shoots. 



Almost every good author now ascribes the potato murrain 

 to the attacks of the Peronospora, and I am glad to see that 

 De Bary is decidedly of the number who do so. It is plain, 

 too, since these moulds are capable of being developed on 

 healthy plants, that they are true parasites, and not the mere 

 consequence of previous disease. 



DESCRIPTION OP THE PIGUEES. 



1. Acrospore of Peronospora parasitica, germinating on 

 glass in a moist atmosphere. 



2. Acrospore of Peronospora infestans, producing septa in 

 the midst of its protoplasm, each division containing a vacuole. 



3. Zoospore, from the same. 



4. Zoospore, from the same, germinating. 



5. Acrospore of Peronospora densa, with its protoplasm 

 oozing out. 



6. Ejected mass, acquiring a membrane and showing 

 vacuoles. 



7. Mass germinating. 



8. Young sporangium and antherid of P. parasitica. 



9. Sporangium, containing a perfect resting- spore. 



10. Resting-spore of Cystopus candidus, ejecting its con- 

 tents, which are in the course of producing zoospores. 



11. One of the zoospores. In Peronospora infestans the 

 two lash-like appendages spring according to De Bary from 

 the same point in the border of the vacuole ; in Cystopus and 

 most Peronosporce from opposite sides of the border. 



All the figures are more or less magnified. 



