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CHAPTER XV 



TRANSLOCATION OF NUTRITIVE MATERIALS 



WE have so far traced the ways in which plants receive 

 their food, and have examined the processes by which it is 

 appropriated. In some cases, indeed in the vast majority 

 of instances, it is constructed in the interior of the plant 

 by certain of the protoplasts from simple inorganic 

 materials which are absorbed from the environment. In 

 green plants this construction extends to all the substances 

 which can be termed food. In plants without a chlorophyll 

 apparatus this construction is partial only, never going so 

 far as the formation of carbohydrates, though, when these 

 are supplied together with inorganic compounds of nitrogen, 

 proteids and fats can be manufactured. In other cases the 

 constructive processes are supplemented by the absorption 

 of food in a suitable condition for nutritive purposes, while 

 in others, again, the last method is the only one observable, 

 all constructive power being absent. 



There are other considerations, which must be briefly 

 stated, which have a bearing upon this subject. The con- 

 ditions of life of an ordinary green plant involve a great 

 extension of the original constructive process. It has no 

 definite and regular times at which it can take in a certain 

 quantity of food, which are regulated partly by the needs 

 of the organism and partly by the mysterious factor which 

 we call appetite. Its absorptive processes are much more 

 under the influence of natural phenomena, such as the 

 degree of illumination, the amount of warmth, moisture, 

 &c., which it is receiving. Periods of intermission of ir- 

 regular duration are caused by differences in these respects, 



