128 SENSITIVENESS OF COTYLEDONS. CHAP II. 



the habit of cotyledons rising vertically at night or 

 going to sleep, and their sensitiveness, especially that 

 of their pulvini, to a touch ; for all the above-named 

 plants sleep at night. On the other hand, there are 

 many plants the cotyledons of which sleep, and are 

 not in the least sensitive. As the cotyledons of 

 several species of Cassia are easily affected both by 

 slightly diminished light and by contact, we thought 

 that these two kinds of sensitiveness might be con- 

 nected ; but this is not necessarily the case, for the 

 cotyledons of Oxalis sensitiva did not rise when kept 

 on one occasion for 1J h., and on a second occasion 

 for nearly 4 h., in a dark closet. Some other coty- 

 ledons, as those of Githago segetum, are much affected 

 by a feeble light, but do not move when scratched by 

 a needle. That with the same plant there is some 

 relation between the sensitiveness of its cotyledons 

 and leaves seems highly probable, for the above de- 

 scribed Smithia and Oxalis have been called sensitiva, 

 owing to their leaves being sensitive ; and though the 

 leaves of the several species of Cassia are not sensitive 

 to a touch, yet if a branch be shaken or syringed 

 with water, they partially assume their nocturnal de- 

 pendent position. But the relation between the sen- 

 sitiveness to contact of the cotyledons and of the 

 leaves of the same plant is not very close, as may be 

 inferred from the cotyledons of Mimosa pudica being 

 only slightly sensitive, whilst the leaves are well 

 known to be so in the highest degree. Again, the 

 leaves of Neptunia oleracea are very sensitive to a 

 touch, whilst the cotyledons do not appear to be so in 

 any degree. 



