The Potato Disease. 509 



ers, enter them tlirou^^h their breathing pores, and begin 

 pushing forth the rudimentary cells of a new mycelium. In 

 short, they are capable of germinating and reproducing the 

 species in just the way of any seed. When they fall upon 

 the soil they are unable to germinate there ; but if brought 

 by rains in contact with the tubers or the fibrous roots, 

 they may enter these and begin their growth at the foot of 

 their host. 



More recently De Bary, one of the most acute and learned 

 of mycologists, discovered in Peronospora infestans a sec- 

 ond mode of reproduction, far more efficient than the one 

 just described. Some of the branches of the fruit stalk of 

 the fungus, instead of bearing on their stalk simple spores, 

 were by him observed to bear, in their places, pod-like bod- 

 ies, since named swarm-spores, because, on the application 

 of moisture, as supplied by dew or rain, they set free a 

 swarm of from six to sixteen other bodies, known as 

 ■zoospores or living spores, so called because they are fur- 

 nished with two cilia, or hair-like tails, by the help of 

 which they are capable of moving rapidly about, like ani- 

 macules. These zoospores are best seen when within the 

 swarm-spores ; for, when once set free, they are, from the 

 extreme rapidity of their movements, very difficult to 

 make out. This rapid movement usually lasts for about 

 half an hour ; and, like the conidia, or simple-spores, 

 before mentioned, these zoospores generally enter the 

 breathing pores of the leaf and there germinate. It may 

 be noticed, in passing, that this genus of fungi takes its 

 name from a peculiar power which its zoospores possess. 

 Peronospora is the Greek for boring seed ; and it is not 



