TRANSLOCATION FROM CELL TO CELL 113 



of the individual cell. Nevertheless, in tissues various ways and means are 

 employed to attain a complete and adequate distribution of necessary 

 materials. Thus substances are frequently transported over considerable 

 distances through dead tissue elements, or through .cell- walls, and when 

 thus transmitted from cell to cell they may reach their goal rapidly, or only 

 after a prolonged journey. Further details of the processes involved and 

 their utility to the plant will be given later (Chap. X), and at the same 

 time the causes inducing and accelerating translocation will be discussed, 

 as well as the restriction of the translocation currents to special paths, as 

 physiological division of labour becomes more pronounced. At this point 

 we are only concerned with the general principles involved in the exchanges 

 between adjacent cells. 



When a substance passes out of one protoplast, penetrates the 

 intervening cell-wall, and is absorbed by an 

 adjacent protoplast, an operation takes place 

 whose general principles have already been 

 recognized in connexion with diosmotic ex- 

 change. This is also the case when the pos- 

 sibility of such exchange and the production 

 of the necessary conditions are due to interacting 

 influences between neighbouring protoplasts. In 

 addition to this, however, we have to consider 

 how, and to what extent, the plasmatic con- 

 nexions which usually, and perhaps always, 

 connect the contiguous living cells of a tissue 

 to one another may be utilized in translocation. 

 These living plasmatic connexions 1 usually pass ^ y t< 5 h v e iew pla ( x 

 as fine threads through tiny pores or canals in 

 the cell-wall, but in some cases, as in sieve tubes, they take the form of 

 coarse and relatively thick strands. 



From general physiological considerations the attainment and main- 

 tenance of harmonious co-operation throughout the plant by the inter- 

 communication of stimuli renders the existence of living continuity so 

 absolutely necessary, that had it not already been discovered its presence 

 must have been assumed, for in no other way could the observed pheno- 

 mena have been explained. It is, moreover, possible that the proto- 

 plasmic communications may aid in the transfer of substances from cell 

 to cell, and even that in special cases their primary function may be to 



1 Kienitz-Gerloff, Bot. Zeitung, 1891, p. i ; 1893, p. 36 ; Zimmermann, Summary in Beihefte 

 z. Bot. Centralbl., 1893, Bd. m, p. 328; and the main literature. See also Wahrhch, Bot. 

 Centralbl., 1893, Bd. LV, p. 368, and Czapek, Sitztingsb. d. Wien. Akad., 1897, Bd. cvi, Abth. i, 

 P- 155- 



PFEFFER 



