590 TRA NSL OCA TION 



their contents escape. In the intact plant, the direction of the currents 

 through the sieve-plates probably varies according to the point at which 

 pressure is applied, and such irregular movements along with the admixing 

 movements in companion cells, &c. are probably of great importance in 

 accelerating the transference of non-diosmosing and diosmosing substances 

 in both directions. This is the main function of the sieve-tubes and 

 phloem, and the existence of a constant upward or downward stream 

 of water would hinder or prevent translocation in the opposite direction, 

 and hence would be a great disadvantage to the plant. 



The exchanges to and from a living cell are primarily determined 

 by its own powers and vital activity, and these are influenced in various 

 ways by the surrounding cells and by the other external conditions. 

 The complicated relationships and interactions involved have already been 

 dealt with as far as possible in Sect. 93, where it has been mentioned 

 that isolated endosperms, cotyledons, pieces of rhizomes or of bulbs, 

 become completely depleted when in contact with sufficient water, especially 

 if the latter is renewed from time to time, for a slight accumulation of the 

 mobilized products apparently suffices to inhibit the further production 

 of diosmosing substances. The diosmotic properties of the protoplast 

 are, however, capable of modification, and hence it is impossible to say 

 in what manner a stoppage of depletion is produced by the action of 

 chloroform or ether, or by the absence of oxygen 1 . Similarly Czapek's 

 observation that translocation ceases in a chloroformed leaf-stalk may 

 have several meanings, and no definite conclusion can be drawn from the 

 fact that the absorption and accumulation of aniline dyes by living cells is 

 not prevented by anaesthetization or by the removal of oxygen 2 . The 

 continuation of translocation in partially plasmolyzed conducting channels 

 simply shows that turgidity is not necessary for the performance of this 

 function. 



Living tissues influence one another not only by the removal of 

 particular substances and by the excretion of others, but also by direct 

 stimulatory actions. Thus enzymes and solvent substances are frequently 

 employed not only to obtain nutriment from dead masses, but even from 

 other organisms or from other organs of the same plant (Sects. 65, 91). 

 The haustorial organs of many seedlings (grasses, &c.) act upon the 

 endosperm of the seed in this manner, but even when absorption is most 

 active, plastic substances may escape in the opposite direction from the 

 endosperm when it is in direct contact with water. The depleted storage 

 receptacles may be more or less completely filled again in the case of 

 rhizomes, bulbs, cotyledons, &c., whereas the endosperm of grasses when 



1 Puriewitsch, Ber. d. Bot. Ges., 1896, p. 210. 



2 Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1896, Bd. IT, p. 284. Cf. Sects. 16, 17. 



