34 Mr. D. Thoday. Experimental Researches on [June 11, 



In the first place, to indicate how universal are the phenomena in greater or 

 less degree, the following selection is given from measurements of a number 

 of leaves of various types. 



Table XIX. — Percentage Decrease in Area (estimated) of various Leaves 



during Insolation. 



August 9, 1908, 6 a.m. to 12 noon. Bright warm day, occasional clouds. 



Cercis, four leaves 1 '6 



1 -6 

 2-4 



2 -0 



Nicofiana, two leaves 1 '8 



4 -4 



Ciicurhita 5 '6* 



Vitis 0-6 



Cherry Laurel, three leaves 1 '2 



1 -2 

 0-9 



August 10, 1908, 8 A.M. to 1.30 p.m. Cloudy, occasional spells of sun.. 



Cucurbita, three leaves f 1 '4 



ri -4 



tl-0 



{I- 



6 



2-5* 



Rheum, two leaves 2 '5 



1 -6 



Sugar Beet, three leaves 0 "6 



1 -7 

 3 -1 



SaxiJ'raffa, with largo thick fleshy leaves... 0 '8 



Shrinkage is sliown by all the leaves examined, though in varying degree. 

 Thus, while Cucurbita decreases in area by 5-6 per cent, Vitin decreases by 

 l)ut 0 6 per cent. Leaves of the same plant may also show considerable- 

 differences from one another (Nicotiana, Sugar Beet), us was Ibuiid to be the 

 case with Ilcliantlms anmtus.'f 



Xerophytic leaves sliow relatively little shrinkage (Cherry Laurel, Vitis, 

 Saxifraga), partly owing to slower evaporation, partly to the mechanical 

 resistance of cuticle and internal strcugtlieniiig tissue to contraction. Where 

 a leaf is also tliick and llesliy {Hiixifnajii) or jjossesses tissue for water storage, 



* TlieBC two rcHultH were given by tlie same leaf, and iifi'ord a relative e.stiniate of the 

 conditions which lield on the two days, 

 t See p. 22, etc. 



