320 REV. G HEKSLOVf OS THE ABSORPTION OF Bill* 



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days, generally many more, before the edges were dead ; and in 

 many cases they rem lined fresh for proloagel periods, even for 



weeks. 



Nor is the result constant with the same kind of leaf. Some 

 old Lilac-leaves had but feeble powers to nourish the parts in air 

 when the apical parts only were laid on water ; whereas leaves 

 taken off the same shoot with the apical part completely im- 

 mersed, or else with the middle part only in water, supplied the 



remaining parts sufficiently. 



As a contrast to the leaf of the Ipomcea mentioned above, 

 another leaf, placeJ with the upper surface of the apical half in 

 water, nourished perfectly the basal part in air, as well as a long 

 stalk. 



Two leaves of Borage were laid, one with the under surface, the 

 other with the upper surface of the apical parts in water ; but they 

 could only nourish the midrib of the part in air ; the sides dried 

 up as far as the rib. 



Both the upper and and under surfaces of Digitalis purpurea 

 nourished the parts in air perfectly. 



In this and other corrugated leaves, the water runs into all the 

 minute channels over the ribs and veins by capillary attraction 

 and thus irrigates the entire surface. Garreau has noticed how, 

 these channels, as well as the one very commonly occurring down 

 petioles, are particularly advantageous for absorbing water. 



The conclusion I have arrived at is that the objection raised is 

 really of no consequence. In the majority of instances it is some 

 days before the margins dry up where the central part only is 

 wet. Moreover similar leaves not kept wet always perish far 

 sooner altogether. This shows that even in leaves least capable 

 of transmitting water laterally, they can do it to some extent; 

 and if the leaves be thick, this is easily effected ; and with corru- 

 gated surfaces the transmission is not only within, but without 

 as well, so that the whole leaf becomes bathed with water, though 

 the apex alone may be actually in it. 



Now, when it is remembered that dew forms all over and on 

 both sides of leaves, they are never in this artificial condition of 

 being wetted only in part, at least at first ; but as the dew dries 

 up in one part of a leaf and transpiration has recommenced in 

 sunlight, the above experiments thoroughly establish the right to 

 believe that an influx will be set up to balance the renewed efllux 

 caused by transpiration. 





