44 



PLANT LIFE. 



to their hosts in various ways. Sometimes the young hypha, 

 growing from a special reproductive body (spore),* so minute 

 that it may easily float in the air and fall upon a leaf, creeps 

 along the surface till it finds one of the 

 microscopic openings in the skin of the 

 leaf, into which it grows (sp, fig. 51). 

 These external openings are connected 

 with irregular spaces between most of 

 the cells of the softer piarts, which are 

 also the parts in which the food-supply 

 is most abundant. In these, therefore, 

 the fungus develops, breaking out to 

 the surface again to form or set free its 

 reproductive bodies. 



Or, the young hyphce may excrete 

 at their tips a substance which so soft- 

 ens or dissolves the cell-walls of the 

 host that they penetrate these cells 

 readily, not only at the surface (sp' , 

 sp" , fig. 51), but in the interior.f They 

 then branch freely, often growing in 

 the spaces between the cells, often 

 passing through the cells themselves 



nbt i fill p' rl ir-itiiiL, thti ^fiu C^\ 

 palls of -1 wood Lei! ( It (. I of ^ ^' J " r 



Plants are often attacked when mere 

 Either from a bit of my- 

 celium or a spore which has survived 

 the winter or the dry season, a h}'pha grows, which, almost 

 as soon as the seedling emerges from the seed, penetrates it. 

 The fungus, in tliese cases, may develop quickly and kill the 



SLOtch pine and destrnvin;,^ 



the primary wall of the cell. 



d e. holes made byhyphK. secdlinslS. 



Magnified about boo diam, ^d 



— After R. Hartic 



* .See ]1 304 .tnd the following. 



f It is not irnproliat-ile tliat the penetration of cell-wall,"; is assisted by 

 such pressure as the gmwint; hypha can exert, but the relative action of 

 enzymes and pressure has nut been determined. 



