1896.J MICROSCOPICAL JOURNAL. 85 



ent we cannot point out any distinct advantage which 

 might be gained by this partnership. 



A number of bog and heath-growing plants illustrate 

 a very interesting form of symbiosis, if it is rightly 

 called so. The roots of such plants as the heather (Erica) 

 and the crowberry (Empetrum), for example, have asso- 

 ciated with them, in fact within their cells, the hyphsB of 

 a fungus, which we here also call mycorhiza, though it is 

 as yet unknown to what fungus the hyphae belong. They 

 occur in quite young cells and from a dense convoluted 

 mass, sending out one or more threads into the surround- 

 ing soil, whence, no doubt, they derive some of their nour- 

 ishment. That the plant makes use of this is beyond all 

 doubt, for one after another these epidermal cells empty 

 the fungal threads of all their contents, and in the older 

 portions of the root nothing but the empty hyph® of the 

 fungus will be seen. These roots seem, therefore, to en- 

 tice the fungus in and then destroy it and live on its 

 contents. 



Symbiosis this is called, but whether the fungus would 

 give it that name I would not like to say. 



In some cases it is not the epidermal, but several cor- 

 tical layers which take part in this exploitation of the 

 micorhiza. That however some mutual benefit does prob- 

 ably take place may be assumed from the fact that is has 

 been impossible to grow the fungus independently of the 

 devouring green plant. 



Another form of root symbiosis is that encountered in 

 the group of the leguminos*, or the pea-tribe. 



On the roots of these you will notice curious swellings, 

 the nature of which was long a puzzle to botanists, but 

 which, though irregularly placed, were of constant occur- 

 ence. (Fig. 6.) Their development was watched, and 

 then it was observed that a fungal spore attached itself 

 to one of the root-hairs, and gave rise to a hypha which 



