408 MODIFIED CIKCUMNUTATION. CHAP. VII. 



much in different species, and seems never to be rigid ; 

 for plants have been introduced from all parts of the 

 world into our gardens and greenhouses ; and if their 

 movements had been at all strictly fixed in relation to 

 the alternations of day and night, they would have 

 slept in this country at very different hours, which 

 is not the case. Moreover, it has been observed that 

 sleeping plants in their native homes change their 

 times of sleep Avith the changing seasons. * 



We may now turn to the systematic list (p. 320). 

 This contains the names of all the sleeping plants 

 known to us, though the list undoubtedly is very 

 imperfect. It may be premised that, as a general 

 rule, all the species in the same genus sleep in 

 nearly the same manner. But there are some ex- 

 ceptions; in several large genera including many 

 sleeping species (for instance, Oxalis), some do not 

 sleep. One species of Melilotus sleeps like a Tri- 

 folium, and therefore very differently from its con- 

 geners ; so does one species of Cassia. In the genus 

 Sida, the leaves either rise or fall at night ; and with 

 Lupinus they sleep in three different methods. Re- 

 turning to the list, the first point which strikes us, is 

 that there are many more genera amongst the Legu- 

 rninosae (and in almost every one of the Leguminous 

 tribes) than in all the other families put together; 

 and we are tempted to connect this fact with the great 



attributing such movements to this effect must be produced on the 

 cause than, for instance, the in- seeds by the long-continued culti- 

 herited habit of winter and vation of the parent-plants under 

 summer wheat to grew best at different climates, but no one pro- 

 different seasons ; tor this habit bably would call this the " Nach- 

 is lost after a few years, like the wirkung " of the climates, 

 movements of leaves in darkness * Pfeffer, ibid., p. 46. 

 after a few days. No doubt some 



