28 THE president's address. 



shoots fall from their axis and root in the ground. Poa 

 stricta is known only in this form, while P. alfina and Festuca 

 ovina are sexual, that is, bear ordinary fertile flowers, in lower 

 countries, but frequently depend on the asexual or viviparous 

 form in high mountains or in the north. 



Thus while in numerous cases adaptation is obvious even 

 when, so to speak, grafted on a primary or even secondary adap- 

 tation, there are large series of forms where we are unable to 

 explain form and structure by any known relationship with en- 

 vironment. Are we dealing here with purely indiscriminate 

 variation or do we merely proclaim our ignorance ? I need only 

 mention the diatoms to suggest an instance of extreme varia- 

 tion in detailed structure for which at present we can find no 

 explanation in adaptation to environment. The great variety 

 in form and sculpturing of pollen- grains and other spores will 

 supply further instances. May I refer to one other case in closing ; 

 namely the colours of the larger fungi which run through almost 

 as striking a gamut as the colours of flowers, but which cannot be 

 explained in a similar way as attractive or otherwise to members 

 of the animal kingdom. We have hitherto regarded this as an 

 example of so-called indiscriminate variation, but recent work 

 indicates that the explanation may be a physiological one 

 associated with nutrition. 



Journ. Quektit Microscopical Club, Ser. 2, 7ol. XIV,, No. 84, April 1919. 



