DISEASES IN GREENHOUSE 91 



peas are minute microscopical forms of 

 plant life, devoid of the green matter 

 known as chlorophyll. Structurally, a 

 fungus consists of one cell or of several 

 cells, connected end to end, forming 

 threads known as mycelium. The fungus 

 gains access to the interior tissue of the 

 plant, and deprives the latter of the food 

 it needs for its welfare. This action re- 

 sults in slow death or in a sudden collapse 

 of the affected host. In the case of pow- 

 dery mildew, mentioned later, the fungus 

 lives on the surface of the leaves, and sends 

 delicate suckers into the epidermis to ob- 

 tain its food from the tissue of the host. 



Parasitic bacteria are smaller forms of 

 life than are the fungi, but their mode of 

 attack is not very different. With the ex- 

 ception of the large mushrooms, which are 

 also fungi, most others are invisible to the 

 naked eye and must be studied under a 



