3 i 4 THE FOOD OF PLANTS 



green, as well as etiolated chloroplastids, have the power of forming starch 

 from sugar or other suitable nutriment 1 . The formation of starch grains 

 appears, as far as is known, to be possible only when suitable chromato- 

 phores are present 2 . The starch grains are generally found in the interior 

 of the chloroplastid, but they may grow until they protrude from it, so that 

 ultimately the coloured or uncoloured starch-forming plastid may simply 

 form a small adhering cap-like body attached to the starch grain (Fig. 47, 

 and Zimmermann, 1894, I.e., p. 92). 



It must be remembered that the chloroplastids are plasmatic organs, 

 and hence necessarily of complicated structure (Sects. 7-11). Even the 

 visible structure of the chloroplastid has not yet 

 been fully studied, but it appears, according to 

 Meyer and Schimper, that the chlorophyll is 

 contained in vacuolar spaces in a colourless proto- 

 plasmic stroma, although it is not yet certain whether 

 the chlorophyll is simply dissolved in an oil im- 

 prcgnating the plastid or is attached in some special 

 manner to the living plasma 3 . It is also doubtful 



whether, as Hansen 4 supposes, the accessory red and brown pigments, which 

 are soluble in water, colour the ground substance of the plastid. In any 

 case all researches upon the influence of the accessory pigments upon the as- 

 similation of carbon dioxide must take into account this possibility (Sect. 60). 



The existence of a certain division of labour in chloroplastids may safely 

 be inferred, and it is possible that pyrenoids are the visible outcome of such 

 functional differentiation, although it is still doubtful whether the pyrenoids found 

 in the large chlorophyll bodies of certain Algae and a few lower plants are 

 functioning elementary organs, or are simply composed of reserve material 5 . 

 The direct protoplasmic connexion with the nucleus which they usually exhibit 

 may point to either conclusion, and, moreover, starch may be formed in other 

 regions of the chloroplastid as well. This stroma-starch seems to be more readily 

 used up than the pyrenoid-starch, and hence the latter behaves more as reserve 

 food-material. 



1 Schimper, Bot. Zeitung, 1880, p. 881 ; Bohm, ibid., 1883, p. 36; Laurent, Bull. d. 1. Soc. Roy. 

 d. Bot. d. Belgique, 1888, T. xxvi, p. 343; Saposchnikoff, Ber. d. Bot. Ges., 1889, p. 259; 

 Zimmermann, Beitrage z. Morph. u. Physiol., 1893, pp. 29, 89. [H. Winkler, Unters. iiher die 

 Starkebildung in den verschiedenartigen Chromatophoren, Jahrb. f. wiss. Bot., 1898, Bd. xxxil, 



P- 5'5-l 



3 A. Meyer, Starkekbmer, 1895, p. 159; Zimmermann, 1894,1.0., p. 92. Belzung (quoted by 

 Zimmermann) states that starch occurs in certain fungi, and moreover no chromatophores or special 

 plastids are necessary for the formation of cellulose. 



3 Cf. Zimmermann, 1894, I.e., p. 90; Zimmermann, Zelle, 1887, p. 59; Keinke, Bot. Zeitung, 

 1886, p. 169; Hansen, Farbstoffe d. Chlorophylls, 1889, p. 86, and Stoffbildung bei den Meeres- 

 algen, 1893, p. 292 (Sep.-abdr. a. d. Mitth. a. d. Zool. Station zu Neapel, Bd. xi). 



* Hansen, 1893, 1. c., p. 301. Cf. Reinke, Bot. Zeitung, 1886, p. 181. 



5 For lit. see Zimmermann, 1894, I.e., p. 93; Klebs, Bot. Zeitung, 1891, p. 793; Chimilewsky, 

 Bot. Centralbl., 1897, Bd. LXIX, p. 277. 



