ALGAL AND FUNGAL PROTISTS 37 



an arrow, the interrupted line showing the level of the soil. 

 If seed is sown thickly on soil half filling a flower-pot and 

 kept well watered and covered by glass nearly all the plants 

 may be affected. Gardeners call this " damping off." 

 Bower describes the last stage thus : " If the cress culture 

 be kept damp for some days longer, a thick felt of hyphae 

 will be formed, which will bind the seedlings together : and 

 finally the disorganisation will spread throughout the seed- 

 lings, causing complete rotting." In a sowing made on 

 sterilised sand I found that no infection occurred. 



Marshall Ward found that a healthy seedling placed in 

 water beside a diseased one was infected in from 12 to 24 

 hours. The hyphae of Pythium are not, like those of Sapro- 

 legnia, content to form an attachment by a rhizoid, they 

 penetrate and traverse the host-cells, Fig. 6, b ; and ramify 

 in and between them and on the surface of the plant. " The 

 cells are killed very shortly after the fungus reaches them, 

 and there is no attempt to react in any way to the invading 

 organism ; no hypertrophy appears nor any attempt at 

 cell-division " (Butler). 



An infected cress-plant placed on a slide shows numerous 

 delicate non-septate hyphate, which after a day or two will be 

 found to have round swellings at the ends of some hyphae 

 and round or oval swellings in the course of (interstitial or 

 intercalar) other or the same hyphae. These swellings at 

 first look very much alike, but soon in some a large vacuole 

 and a beak-like process of the inner wall develope, Fig. 6, e, 



