426 STORAGE SYSTEM 



whole, or, at anyrate, by extensive portions of the plant-body. A few 

 words may be added with reference to local storage-tissues, which serve 

 for the nutrition of individual organs or tissues. According to 

 Tschirch and Holfert, the so-called " nutritive layer " which is found in 

 many seed-coats during the ripening of the seed, represents such a 

 local storage-tissue. 199 It usuallv consists of several tangential rows of 

 cells containing abundance of starch, and is situated in the immediate 

 proximity of the elements which later give rise to mechanical tissue or 

 to mucilage-layers. The plastic materials required, in either case, for 

 the deposition of thickening layers upon the cell-walls, are derived from 

 the nutritive layer. The latter is, hence, entirely depleted when the 

 testa is fully developed, and, as a rule, ultimately disappears 

 altogether, its former position being indicated in the ripe seed by a 

 zone of compressed and distorted cell- walls. Excellent examples of 

 these nutritive layers are to be found among the Papilionaceae and 

 Cruciferae. 



2. The storage of respiratory material. 



The plastic material deposited in storage-cells never becomes 

 wholly incorporated in the growing tissues ; a certain proportion 

 thereof is always destined to undergo katabolic change. This portion 

 is set apart to serve as respiratory material, to provide the fuel for the 

 " physiological combustion " which results in liberation of chemical 

 energy, and often also in evolution of heat. Boussingault long ago 

 noticed that seedlings of Indian Corn, when grown in the dark, lost 

 47*6 per cent, of their dry weight in the course of twenty days, 

 mainly as a result of respiration. 



So far as is known, " respiratory " reserve-materials are not, as a 

 rule, deposited separately from those which are destined to be utilised 

 in connection with growth ; in other words, there are no special 

 storage -tissues set apart for the general mass of respiratory materials. 

 In a few exceptional cases, however, where the liberation of heat is an 

 essential, and not merely an incidental, feature of the respiratory 

 process, storage- tissues may be developed for the reception of calorific 

 material, in the form of starch or other carbohydrate substances. It 

 has long been known, that certain flowers and inflorescences evolve a 

 very considerable amount of heat when they first open. The most 

 striking illustrations of this phenomenon are furnished by certain 

 Aroideae.' 200 In the case of Arum italicum, for example, Gregor Kraus 

 bas recorded a temperature of 44*7 C. in the spadix, as compared with 

 an external temperature of 17'7C; here there is a difference of 27 ( \ 

 in favour of the plant. The maximum temperature observed by 

 Hubert during a series of observations upon Colocasia odora was as 



