T 14 THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



act as translocatory channels for nutritive and plastic materials. The 

 plasmatic threads may also serve for the transmission of living material or 

 of stimulating substances from one part to another, the threads here acting 

 as the channels along which stimulatory influences flow. 



In order to attain a rapid power of translocation, these plasmatic 

 threads are not absolutely essential, and they have nothing at all to 

 do with the actual entry of substances from the external world, or with 

 the final exit of excrete metabolic products, and yet both excretion and 

 absorption can take place to an adequate extent. In the germination of 

 Zea mats, the store of reserve food material is absorbed by the superposed 

 scutellum as rapidly as it becomes soluble, so that in this case relatively 

 rapid translocation is possible without the aid of any interprotoplasmic 

 connexion. It is therefore clear that substances may be directly trans- 

 located in internal tissues from cell to cell through the intervening cellulose - 

 walls as rapidly as the limits of safety and economical transport will allow. 

 When such repeated transference from cell to cell takes place through 

 separating walls, the length of the series through which the current is 

 passing has no influence upon the rapidity with which substances are 

 transferred from any cell to those immediately adjacent to it, for each 

 cell has its own special potential energy of absorption, determined by 

 its specific powers of passive secretion. (See Sects. 22 and 108). 



Cells can absorb a variety of substances, including colloids, while oils 

 may pass unaltered through the cell-wall and plasma membrane (Sects. 

 16-19). Other examples of rapid absorption and accumulation of sub- 

 stances have already been given (Sects. 16 and 22). Aniline dyes also 

 may be observed to be transferred with normal rapidity from cell to cell 

 without the aid of interprotoplasmic connexions. 



Diosmotic transmission is not only sufficient for all necessary trans- 

 ference, but is actually employed in translocation, although it is possible 

 that the plasmatic connexions may play an important accessory part. 

 The latter is certainly the case in sieve tubes (Sect. 106). though it does 

 not necessarily follow that the finer plasmatic connexions are of equal 

 importance. In these, in spite of their minute sectional area, transference 

 is possible by the aid of pressure or as a vital process, and, indeed, it is 

 even possible for living plasmatic masses to penetrate through cell-walls 

 in which no pre-existent openings are present (Sect. 19). It can hardly 

 be doubted that for particular purposes, and to attain special ends, 

 plasmatic elements or masses may pass from one cell to another. There 

 are, however, no observations in favour of the view that such transference 

 is of importance in the translocation of nutritive or excretory substances 

 from one cell to another. Were the latter the case, the fineness of 

 the threads would render necessary extremely active streaming currents 

 directed both towards the interior and the exterior of the cell ; and to 



