STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 33 



In later communications by Schimper (Botanische Zeit., 1883, xli, 121; JahrbUcher 

 f. wiss. Bot. 1885, xvi, 7) studies are made especially of the origin and functions of chlo- 

 rophyl-grains anil homologous structures. Leucoplasts, he writes, originate in the vege- 

 tating cells of the plant, and but rarely from chloroplasts. Certain fruits which are green 

 in the young stages and white in the mature condition contain leucoplasts which develop 

 from the chloroplasts, as, for instance, in the white fruit of the snow-berry, Symphoricar- 

 pus racemosus. Leucoplasts are widely distributed and serve as starch-builders; rarely are 

 they functionless, as in the roots of Dahlia. Many leucoplasts may be transformed into 

 chloroplasts, especially when they are exposed to light of sufficient intensity, but some 

 leucoplasts are incapable of this change. In non-chlorophyllous starch-producing plants, 

 or parts of plants, the starch is formed by leucoplasts. 



Referring to chromatophores, Schimper records that they assume very different forms, 

 and that it is difficult to discover an external relation between them. The green tabular 

 chloroplasts, the colorless (usually very deUcate) spherical leucoplasts, and the chromoplasts 

 with manifold forms differ widely from each other. Nowhere is the capacity shown by liv- 

 ing substance to assume such diverse forms and properties as is exhibited by these simple 

 protoplasmic structures. One and the same chromatophore, as a leucoplast, can form and 

 store up starch from assimilated materials, or as a chloroplast can decompose carbonic acid 

 and produce organic substance from carbon and water, or as a yellow or red chromoplast 

 can fill the passive role of attraction for animals. Chromatophores originate exclusively 

 from preexisting chromatophores. In the simpler plants, as in Chlorophyccce and Diato- 

 macece, leucoplast formation is a subsequent process, that is, cliromatophores which con- 

 tain pigment are transformed into colorless chromatophores, or leucoplasts; but in higher 

 plants the opposite process takes place. This condition in the simplest plants leads to the 

 belief that leucoplasts are to be regarded as metamorphic forms of pigmented, assimilating 

 chromatophores. The chromatophores of a large number of Angiosperms form protein crys- 

 tals, and the shape of the chromatophore is often due to the presence of these crystals, and 

 thus the shape and structure of the starch-grain are correspondingly influenced. In Phaius 

 (orchid), starch-grains are produced which have an eccentric structure and some are tri- 

 angular in shape. These are developed on an elongated chromatophore, the elongation 

 being due to the presence of protein crystals. 



That these crystals thus indirectly influence the shape of starch-grains is also shown 

 in the rhizomes of some Zingiberacea;. In such plants the chromatophores of the rhizomes 

 always produce elongated, spindle-shaped, or needle-like crystals, and these cause the odd 

 structure of the starch-grains. In the rliizomes of Canna, large, flattened, triangular, mark- 

 edly eccentric starch-grains develop. These grow on leucoplasts which form two kinds of 

 crystals — flattened octohedra and needle-like. The grains lie both on and within the chro- 

 matophores, and in the latter location attain an eccentric structure which is influenced by 

 the presence of crystals. Colorless bodies, pyrenoides, are found in the chromatophores of 

 many Algce, and appear to act as nuclei of the chromatophores. They bear a close relation 

 to starch-formation. In these plants, the starch-grains which originate within the chromato- 

 phores appear first and in the largest numbers about the pyrenoides, which they surround 

 in the form of a shell. Observations indicate that the pyrenoid substance is in the nature 

 of a reserve material that is used by the chromatophore in starch-building, and that they 

 are probably crystals, since they behave like protein crystals of the higher plants. 



Schimper also believes that in young cells of certain of the lower plants, cell nuclei 

 furnish material for starch-formation before the chromatophores are developed; but sta,rch 

 subsequently appears everywhere in the cells about the chromatophores, by which time 

 the nuclei apparently have ceased to yield starch-forming material. 



Chloroplasts and pyrenoids in Algw, chloroplasts and paramylum bodies of Euglena;, 

 and pyrenoids in bacilli were reported by Schmitz (Die Chromatophoren der Algen, 1882; 

 Jahr. f. wiss. Bot. 1884, xv, 1). 



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