112 PULVINI OF COTYLEDONS. Chap. II. 



cotyledons which at noon were nearly horizontal, stood 

 at night at more than 20° and less than 60° above the 

 horizon, they were recorded as " plainly raised ;" and 

 of such genera there were 38. We did not meet with 

 any distinct instances of cotyledons periodically sink- 

 ing only a few degrees at night, although no doubt 

 such occur. We have now accounted for 64 genera 

 out of the 153, and there remain 89 in which the 

 cotyledons did not change their position at night by 

 as much as 20° — that is, in a conspicuous manner 

 which could easily be detected by the unaided eye and 

 by memory; but it must not be inferred from this 

 sta,tement that these cotyledons did not move at all, 

 for in several cases a rise of a few degrees was re- 

 corded, when they were carefully observed. The 

 number 89 might have been a little increased, for the 

 cotyledons remained almost horizontal at night in 

 some species in a few genera, for instance, Trifo- 

 lium and Geranium, which are included amongst the 

 sleepers, such genera might therefore have been added 

 to the 89. Again, one species of Oxalis generally 

 raised its cotyledons at night more than 20° and less 

 than 60° above the horizon ; so that this genus might 

 have been included under two heads. But as several 

 species in the same genus were not often observed, 

 such double entries have been avoided. 



In a future chapter it will be shown that the leaves 

 of many plants which do not sleep, rise a few degrees in 

 the evening and during the early part of tlie night ; 

 and it will be convenient to defer until then the 

 consideration of the periodicity of the movements of 

 cotyledons. 



On the Pulvini or Joints of Cotyledons. — With several 

 of the seedlings described in this and the last chapter, 

 the summit of the petiole is developed into a pulvinus, 



