1041 



the winter can be distinguished by the microscope from one cut at 

 any other period. This deposit being formed in the autumn, may be 

 called the autumnal deposit. This is one of the earhest parts in 

 which, at the commencement of spring, a process of elaboration is 

 seen to begin : as this process is going on, the granular matter disap- 

 pears, and the cells become of an irregular figure and filled with 

 fluid : still later these cells become broken up, and their place occu- 

 pied by vessels and ligneous cells. The distension of these cells 

 with fluid, and their consequent breaking up, is the cause of that 

 loose connexion between the wood and the bark, so remarkable in the 

 branches of most trees at the spring of the year. The foliaceous 

 organs having made these provisions for the future, and fulfilled all 

 the purposes for which they were designed, now become useless; and 

 the process of elaboration ceasing in their cells and vessels, they at- 

 tract no more crude sap, become withered, and unfit to be retained 

 on the tree, and are therefore shed ; and the plant experiences a state 

 of repose, the duration and completeness of which varies in different 

 kinds of plants." — p. 27. 



Mr. Rainey then proceeds to explain the ascent of elaborated sap. 

 It having been ascertained that starch is deposited in the roots while 

 the leaves are in active operation, and that this starch is undoubtedly 

 designed for the supply of leaf-beads ; it becomes necessary j^r«^, that 

 the starch or its elements be so changed in physical properties as to 

 be capable of being conducted to the part requiring to be nourished; 

 and secondly, that they be so propelled as to reach such parts. The 

 author's idea is that the starch is dissolved in the water imbibed fi-om the 

 earth by capillary attraction, and that this supply continues to press 

 upwards the fluid already in the vessels of the stem, branches, and 

 finally of the developing leaf- buds. Tliis seems to require fiuther ex- 

 planation : the ascent of fluid in a previously empty capillary tube is 

 supposed to be caused by its very emptiness ; load a sponge with water 

 and capillary attraction ceases : squeeze out the water and it recom- 

 mences immediately : on the same principle is it not requisite that the 

 sap already in the branches and buds should escape before capillary 

 attraction can act so powerfully at the root as to drive all upwards in 

 the way described ? We merely suggest this for the author's conside- 

 ration : we do not venture to ground an objection to his views on this 

 seemingly insufficient explanation. The author himself is aware that 

 the plant with unexpanded leaves has no means of getting rid of the 

 superfluous water, and he says that in consequence the vessels become 

 distended. When an incision is made in the bark (especially of the 



