36 



OUTLINES OF PLANT LIFE. 



which so softens or dissolves the cell -walls of the host that 

 they penetrate these cells readily, not only at the surface 

 (j/', sp" , fig. 32), but in the interior.* They then branch 

 freely, often growing in the spaces 

 between the cells, often passing through 

 the cells themselves (fig. j,'^. 



Plants are often attacked when mere 

 seedlings. From either a bit of my- 

 celium or a spore that has survived 

 the winter or the dry season, a hypha 

 grows, which, almost as soon as the 

 seedling emerges from the seed, pene- 

 trates it. The fungus, in these cases, 

 may develop quickly and kill the young 

 plant (as in the "damping off" disease 

 in greenhouses), or it may develop slowly 

 and not reach its maturity until the host 

 is also mature. 



46. Haustoria. — Those fungi which 

 grow upon the surface of living plants 

 (and those which grow in the internal 

 air-spaces) often have special branches 

 for fastening themselves to the host or 

 Fig. 33.- Hypha of T-ra- absorbing food from it. In the surface 



tnftes Pini perforating at c . 



the walls ot a wood-cell of fungi these are usually very short, disk- 

 Scotch pine and destroying 



the primary wall of the cell, like Or lobcd branches which do not 



(/, e, holes made by hyphse. 



Magnified about 800 diam. penetrate the cclls of the host. In 



—After R. Hartig. 



Other cases they are branches of minute 

 diameter, which enter the cells, and either enlarge into a 

 knob (fig. 34) or branch profusely (fig. 35). 



* The penetration of cell-walls is probably assisted by such pressure 

 as the growing hypha can exert. 



