THE TRANSLOCATION OF THE ASH CONSTITUENTS 585 



the shrivelling of the leaf or its fall prevents many substances from being 

 conveyed to the parent plant, which are liberated only at death. 



In those organs which are not used for storage, the accumulated 

 calcium remains for the most part permanently deposited. This is 

 the case for example in foliage- leaves in which the absolute amount of 

 calcium, and of silicon also, continually increases until the death of the 

 leaf, whereas when the latter is adult the absolute amounts of phosphorus, 

 potassium, magnesium, and nitrogen, remains comparatively constant, 

 although a certain decrease often occurs when the vitality of the leaf 

 declines, or even before this, owing to the economic transference of a portion 

 of these elements to the parent plant 1 . In such cases a portion of the 

 living protoplasm may be decomposed and translocated, or even directly 

 consumed. The constancy of the percentages of phosphorus, potassium, 

 &c. in the adult leaf can only be the result of unceasing exchanges, for 

 the transpiration-current continually carries fresh supplies to it. These 

 elements are probably conveyed to the stem along with the assimilatory 

 products and probably partly in the form of proteid substances, while, as 

 might be expected, no constant relationship exists between the percentages 

 of phosphorus, nitrogen, &c. (Sect. 74). 



The period during which the production (or absorption) of organic 

 substance is most active, does not necessarily precisely coincide with the 

 period of maximal absorption of ash constituents, but nevertheless a certain 

 indirect relationship exists between the accumulation of organic and of in- 

 organic materials. Translocation may, however, be active without involving 

 a marked increase in the dry weight, and this is always the case when the 

 production is equalized by the consumption, while even in dying plants 

 or in isolated parts or organs nutritive materials may still be conveyed 

 from one region to another. Thus the fruits of cereals withdraw all the 

 available materials from the surrounding parts of the inflorescence even 

 after the ear has been removed from the parent plant 2 . Cereals under 

 normal conditions appear to have accumulated a sufficient supply to 

 complete their development before flowering is over, and hence if plants 

 grown in a nutrient solution are then removed to pure water, normal fertile 



1 Wehmer, Landw. Jahrb., 1892, Bd. xxi, p. 513, and Ber. d. Bot. Ges., 1892, p. 152 ; Zoller, 

 Versuchsst., 1864, Bd. VI, p. 231; Rissmuller, ibid., 1874, Bd. XVII, p. 17; Dulk, ibid., 1875, 

 Bd. xvm, p. 188; Fleche et Grandeau, Ann. d. chem. et d. phys., 1876, v. sen, T. viu, p. 486; 

 Passler, Chem. Centralbl., 1893, n, p. 654. On the leaves of evergreens, cf. Briosi, Bot. Jahresb., 

 1 888, p. 23. On the behaviour during premature leaf-fall caused by summer drought, see G. Kraus, 

 Bot. Zeitung, 1873, p. 401, and the criticisms of Wehmer, I.e. 



3 Literature : de Candolle, Pflanzenphysiol., Bd. II, p. 182 ; Lucanus, Versuchsst., 1862, Bd. iv, 

 p. 147; Siegert, ibid., 1864, Bd. vi, p. 134; Heinrich, Ann. d. Landw., 1871, Bd. LVH, p. 31; 

 Nowacki, Unters. liber das Reifen d. Getreides, 1870; Nobbe, Versuchsst., 1874, Bd. xvil, p. 277; 

 Balland, Bot. Jahresb., 1888, p. 42 ; Holfert, Flora, 1890, p. 281 ; Hotter, Versuchsst, 1892, Bd. XL, 

 P- 356- 



