1879] TRANSACTIONS. ^ 



the tip, by a very delicate fuzz made up of extremely fine hairs. 

 These are the root-hairs, which serve to take up the water-food 

 for plants. They are so exquisitely delicate that the slightest 

 touch crushes them ; and, if the plant is lifted from the soil, all 

 the root-hairs are left behind, or else a few hold fast to finer 

 particles of soil which are brought away. 



Of course, a microscope is very necessary in any careful 

 examination of root-hairs ; but the hairs can be seen without 

 one in the cases mentioned, and in some others, where they are 

 looked for carefully. It is these root-hairs, and not the very 

 tips of the roots, which absorb water. This can be studied 

 practically in the way pointed out by Ohlert, a German school- 

 teacher, who first published, in 1837, an account of root-hairs. 

 The tips may be carefully removed, and the wounds painted 

 over, and the roots placed again in water, where the hairs can 

 have a chance to absorb, if this is their office. 



Root-hairs are found only on the newer parts of roots ; and 

 these are, therefore, the only active absorbents of dilute aqueous 

 solutions." 



By the root-hairs, dilute solutions are carried up from the soil 

 to green tissue upon the younger stems and in green leaves. 

 Here the dilute solutions become more concentrated by evap- 

 oration and transpiration, a process which in the leaf is governed 

 largely by delicately balanced valves which are chiefly on their 

 under surface. " Within the tissue of green leaves, there can 

 be found granules of a leaf-green substance. Under the influ- 

 ence of sunlight, carbon dioxide, a gas which exists as an 

 impurity in the atmosphere, and .which is readily taken up by 

 green leaves, undergoes, together with the water within the leaf, 

 changes which end in the formation of starch or something 

 very much like it. While such an operation is going on, 

 oxygen is given off by the leaves. The relations of oxygen 

 and carbon dioxide to animal respiration are to be pointed out 

 to the pupils ; and it is to be made clear that the evolution of 

 oxygen from green leaves, goes on only in the light. In all its 

 kinds of activity, except that of leaf-green in sunlight, the 

 plant takes in oxygen and gives off carbon dioxide. But the 

 work of leaf-green in sunlight, namely, the conversion of inor- 

 ganic matter into organic substance, is the chief work of the 

 common plants about which we have been studying. This work 

 is assimilation. 



The assimilated product made by green leaves in sunlight is 

 stored up in many forms and in many places, such as roots. 



