36 THE MECHANICS OF GROWTH 



any time a solution or a renewed deposition of starch may occur 1 . 

 A starch-grain does not dissolve solely from the outer surface, but also 

 from within, so that frequently a skeleton of the grain is produced. 

 Typical sphaerocrystals often dissolve in an equally peculiar manner 2 , 

 and changes in the conditions during their formation may result in the 

 production of denser layers than those first formed 3 . 



The shape and growth of a starch-grain depends upon a variety of 

 factors, such as the specific character and activity of the amyloplastid 

 (leuco- or chloroplastid), the position of the starch-grain in it, and also 

 upon a number of circumstances which influence these relationships and 

 others also (Meyer, I.e., p. 172). Hence the starch-grains in the same 

 cell are not always precisely similar, and in diversely differentiated cells 

 of the same plant they may assume widely different shapes, as for 

 example are those in the laticiferous cells of Euphorbia when compared 

 with those in other cells of the same plant. Usually the starch-grain 



only continues to grow so long as it is in con- 

 tact with the plastid, and -when the latter is 

 attached to one side only, growth takes place 

 in this direction and an excentric lamellation 

 results (Fig. 10). The enlarging starch-grain not 



FIG. 10. Chloroplastids from the i 1 . ., .. i_ i_ r j_i 



stem of Peiiionia Daveauana show- only regulates its own growth by means of the 

 e^enufc^tk'rch-grSn capped^*" distension and shifting of the bulk of the plastid 



flattened chlorophyllous plastid. .... . . ',1 r 



which it causes, but also, as in the case of a 



growing crystal, the part already deposited influences the shape of the 

 subsequent additions 4 . 



The fact and arguments brought forward by Meyer (1. c., pp. 13, 154) do 

 not entirely dispose of the possibility of a certain amount of intussusception 

 occurring in starch-grains, for even in a typical sphaerocrystal an interpolation 

 of new particles may take place without the volume of the crystal appreciably 

 increasing. The fact remains, however, that the main growth of the starch- 

 grain takes place by the apposition of new layers, and hence all of Nageli's 

 arguments which were based upon the contrary hypothesis fall to the ground. 

 According to Meyer (1. c., p. 147), the inner layers of the starch-grain become 

 more watery after they have been deposited, whereas Schimper (1. c.) concludes 

 that the differentiation is present at the outset, the particles in the older layers 

 being deposited closer together. Meyer (1. c., pp. 155, 245) has, however, 



1 On the solution and re-formation of starch-grains cf. Vol. I, pp. 318-320, 326, 473. On the 

 mode of solution cf. A. Meyer, 1. c., p. 228 ; Salter, Jahrb. f. wiss. Bot., 1898, Bd. xxxn, p. 164. 



2 Hansen, Arbeit, d. Botan. Instituts in Wiirzburg, 1884, Bd. ill, p. no. 



3 A. Meyer, 1. c., p. 100 ; Bot. Ztg., 1896, p. 328 ; Lehmann, Molecularphysik, 1888, Bd. I, 

 p. 354. On the so-called artificial starch-grains see Biitschli, Ueber die Herstellung von kiinstl. 

 Starkekornern, 1896; Unters. iiber Structuren, 1898, p. 239; Rodewald and Kattein, Zeitschr. f. 

 physikal. Chem., 1900, Bd. xxxni, p. 579. 



* A. Meyer, I.e., p. 167 ; Rothert, Ber. d. Bot. Ges., 1897, p. 236 ; Salter, I.e. 



