316 MODIFIED CIECUMNUTATION. Chap. VL 



ledon of Trifolium, strietwm, in combination with that 

 of the first true leaf. Lastly, the wide distribution in 

 the dicotyledonous series of plants with cotyledons 

 which sleep. Reflecting on these several facts, our 

 conclusion seems justified, that the nyctitropic move- 

 ments of cotyledons, by which the blade is made to 

 stand either vertically or almost vertically upwards 

 or downwards at night, has been acquired, at least 

 in most cases, for some special purpose ; nor can wc 

 doubt that this purpose is the protection of the upper 

 surface of the blade, and perhaps of the central bud 

 or plumule, from radiation at night. 



