FUNGI, WATER MOLDS 



283 



the horticulturist or farmer. Some of the important diseases 

 caused by them are downy mildew of the grape and cucumber, 

 onion blight, early potato blight,* etc. During 1849 tne potato 

 blight caused almost the complete loss of the potato crop in 

 Ireland, and a serious famine resulted. 



428. The mycelium. The mycelium attacks the leaves, 

 stems, and fruit. The germ tube from a spore enters at a stomate 



Fig. 227. 



Intercellular mycelium with haustoria entering the cells, 

 rust); B, of Peronospora calotheca. (De Bary.) 



A , of Cystopus candidus (white 



of the leaf or between epidermal cells. The mycelium grows 

 between the cells in the intercellular spaces, and is thus said to 

 be intercellular. The mycelium is continuous and multinucleate. 

 It develops short special branches, of different form in different 

 species, which penetrate the cells and take food from the proto- 

 plasm (fig. 227). This kills the cells, and dead spots appear on 

 the leaves, fruit, and stems, or the death of leaves, fruit, and 

 stems is the result in some cases. 



* The remedy for these blights is to spray the plants with Bordeaux mixture 

 before they become infested. Spray when the leaves are young, and then at 

 intervals of two to three weeks. In the case of the grape vine the first spray 

 should be applied before the buds burst. 



