no SCIENCE PROGRESS. 



repair of the actual framework is not so great as that of the 

 animal, but the continual formation of fresh material is com- 

 paratively greater. Growth, though slow in plants, taken 

 as a whole, is nevertheless much more prolonged, and year by 

 year sees also the formation of new substance to replace that 

 cast off by reason of the changes of the seasons. The con- 

 ditions of life are so different and the intermittence in the 

 absorption of material so much more irregular that we must 

 expect the whole story of metabolism to run upon different 

 lines, though the ultimate nutritive processes may show a 

 very close correspondence. The tendency of plants is to 

 accumulate stores of material on which their protoplasm 

 may subsist and from which they may construct their new 

 substance. Long periods often occur in their lives during 

 which their constructive powers are in abeyance, and as then 

 no absorption of their food-stuffs can take place they must 

 subsist on the stores they have been able to accumulate 

 in more favourable times. The materials which thus are 

 found deposited in their tissues have been called generally 

 their reserve materials, and a great part of their metabolism 

 is directed towards an accumulation of these. 



We are apt, perhaps, in using this term reserve materials 

 to think only, or chiefly at least, of those stores which we find 

 laid up in seeds, tubers, or other parts to carry them over a 

 period of absolute quiescence. This thought, however, falls 

 short of the actual needs which they show. When we con- 

 sider the processes of growth and repair we recognise that 

 these are largely local and that the localities are many 

 and widely distributed in the organism. The activity varies 

 very much in these various regions from time to time, and 

 with this variation arises the necessity for a continual cir- 

 culation of the nutritive material about the plant. Besides 

 the stores of food-stuffs deposited in the various reservoirs 

 we can discover, we must recognise a circulating store, flow- 

 ing sometimes in one direction and sometimes in another, 

 consisting to a certain extent of the same materials as the 

 quiescent reserves, but generally in a more plastic form, 

 fitted, that is, for the immediate use of the living substance. 

 Indeed the utilisation of the deeper reserves depends upon 



