Reserve Material of Plants. 195 



ject only to a daily periodicity, due to alternation of day and 

 night. As fast as formed, the starch is disposed of in two ways : — 



(1 ) It is transferred in a soluble form to all the actively growing 

 parts of the plant to meet the immediate requirements of growth. 

 So long, therefore, as vegetation, or the extension of tissues is 

 active, the bulk of all the starch produced is at once disposed of 

 in this way, and there is therefore no excess, but all the tissues 

 show a marked absence of it. This is particularly true during 

 the first one or two months of spring and summer, the solution 

 of the stored starch commencing at a period which antedates 

 the first growth ; but as the season advances, maturity of parts 

 replaces rapid extension, and then there is a tendency for the 

 starch to be formed in excess of the immediate demands of growth, 

 and it therefore requires to be disposed of otherwise. 



(2) The starch produced in excess of immediate needs 

 is transferred in a soluble form to parts of the plant which 

 have generally lost their power of growth and which 

 contain no chlorophyll, and is there deposited until required by 

 the growth of organs at some future period, generally before the 

 leaves have reached that stage of development which will permit 

 of their assimilating new material. In accordance with this it is 

 generally found that there is comparatively small accumulation 

 of starch in the leaves and other assimilating tissues, while any 

 excessive development there becomes at once indicative of dis- 

 ordered function. 



It is impracticable to place a quantitative limitation upon the 

 amount of starch which may normally be present in tissues, and 

 apply that law to all periods of vegetation ; the limit can only be 

 established as a matter of experience, since in early summer, when 

 growth is most active — the requirements of tissue-formation 

 keeping pace with the power to supply — the tissues all contain 

 a minimum of starch ; but toward the end of summer, as growth 

 ceases, there is a tendency to greater accumulation in all the tissues. 

 At the end of the season, as the leaves ripen previous to their annual 

 fall, whatever starch they contain is either withdrawn to the per- 

 manent structure of the plant, or it enters into fatty degeneration. 

 Such changes ate normal. If, on the other hand, such accumula- 

 tions or fatty degenerations occur at other than their normal period, 

 or if in excess at this time, as fatty degeneration during the month 



