DISEASES IN GREENHOUSE 115 



aids the fungus in its destructive work. 

 Thielavia basicola also attacks a number 

 of hosts other than the sweet pea. Pure 

 cultures of the fungus obtained from cow- 

 pea, violets, parsnip, and tobacco, when 

 inoculated on the sweet pea will readily 

 infect the latter. This shows that the dis- 

 ease will cross from other hosts to the sweet 

 pea and vice versa. 



The Fungus. The mycelium of Thie- 

 lavia basicola is hyaline, septate and 

 branched. The mycelium becomes some- 

 what grayish with age. Three kinds of 

 spore forms are produced — endospores, 

 chlamydospores, and ascospores. Endo- 

 spores are so called because they are formed 

 inside a special thread of the mycelium 

 (fig. 14<2). This is the spore form that 

 commonly occurs in pure cultures of arti- 

 ficial media and ori the host. The endo- 

 spore case is formed on terminal branches 



