396 STORAGE SYSTEM 



of the conducting system especially conducting parenchyma, the sub- 

 sidiary cells of stomata, etc. In the majority of such instances for 

 example, in the case of bast-fibres which contain starch -grains, storage 

 is most naturally regarded as a subsidiary function of the tissue or 

 tissue-system involved. Sometimes the tissue or system may be con- 

 sidered as having undergone a temporary change of function ; this is 

 perhaps the correct interpretation of the presence of starch in the 

 hadrome-parenchyma and the medullary rays. Strictly speaking, this 

 aspect of storage does not fall within the scope of the present chapter. 

 We shall confine our attention to the most typical form of storage, 

 namely, that which involves the differentiation of a special storage- 

 tissue ; no tissue should therefore be termed a storage-tissue unless 

 its principal function is the accumulation of a store of reserve 

 materials. 



It has already been stated, that the stored-up synthetic products of 

 the plant consist in the main of plastic materials, reserved for consump- 

 tion during succeeding phases of growth. These substances constitute 

 reserve -materials, in the strict sense, such as may be met with more 

 particularly in seeds, fruits, bulbs, tubers, rhizomes, and other organs of 

 propagation or hibernation. In other cases, the accumulated synthetic 

 products may be largely or exclusively utilised as respiratory materials. 

 Further, storage is not always connected with strictly physiological 

 requirements ; ecological considerations may also lead to the deposition 

 of reserve-materials in particular cells or tissues. Thus, various organic 

 compounds are deposited in succulent fruits, in floral organs and so 

 forth, in order to provide an attraction for animals, which in return 

 perform some service on behalf of the plant in connection with seed- 

 dispersal, cross-pollination or protection. Tissues and structural features 

 which are concerned with ecological relations of this nature, may be in- 

 cluded in a comprehensive definition of the storage system ; they will 

 be dealt with in a special section at the end of the present chapter. 



Many propagative organs, such as bulbs and tubers, contain not 

 only a supply of synthetic products but also a store of water, 

 so that they are able to resume active growth even in a dry 

 soil. Every gardener is familiar with the fact that many bulbs will 

 sprout, even when they are hung up in a dry atmosphere. In such 

 cases as these, the stored-up water is just as much a reserve-material 

 as the accumulated supplies of starch or protein ; for, in the building 

 up of the plant-body, a sufficiency of water is no less indispensable 

 than a proper supply of plastic material. 



The acquisition, by one means or another, of a store of water may 

 be of advantage to a plant in its fully developed state, as well as at 

 the start of its vegetative life. Many xerophytes, in fact, depend for 



