'IHI-: AM I KIC \\ I'.o'l'.W'IST 165 



growth till the up])er and lower sides of the i)etioles ur of the 

 blade or of hoth, preceded |)robal)l\- h\- the increased tur- 

 gesceiice o| tlie growing cills. 



'{'here i^ an iiuleiieiulence ol ilie iioctnrnid nio\enients of 

 the leaves and cotxledons on the >anie phmt. and (vn plants i)e- 

 longing to the same genns. 'rhi> leads to the l)elief that the 

 cotyledons have ac<iuired their power of nioxenient for some 

 sj)ecial pnrpose. Other facts lead to this same conclusion, 

 such as the presence of pulvini. hv the aid of which noctur- 

 nal movements are continued during st)me weeks. 



The cotyledons of some species move vertically upwards 

 and others vertically downwaid at night; while in others one 

 cotyledon ino\es upwards while another moves downward. 

 Biologists are justified however, in assuming that the move- 

 ments have l)een ac(|uired at least in most cases, for some 

 special purpose; nor can we doubt that this purpose is the pro- 

 tection of the upper surface of the blade and perhaps of the 

 central bud from radiation at night. All gardeners know that 

 [.lants suffer from radiation. It is this and not the cold winds 

 that the peasants of Southern iCurope fear for their olives. 

 Jt is a known fact that a thermometer rises as soon as a fleecy 

 cloud, high in the sky, passes over the zenith. Seedlings are 

 often protected from radiati( n by a ver>- thin covering of 

 straw, and fruit tree> on wall- by means of a few fir branches, 

 or even a thin netting spread over them. Fruit growers place 

 smudge pots in their orchards in order to protect the buds. 



Many flowers close at night, and these are likewise said 

 to sleep. Their movement is effected by the same mechanism 

 as in the case of yoiuig leaves; namely une(|ual growth> on 

 opposite sides, yet they differ essentially in being e.xcited chieHy 

 by changes in temi)erature instead <»f liglit. W-rv likely they 

 close at times when the pollen is liable to become destroyed, 



