3l6 LECTURE XIX. 



the chlorophyll-corpuscles in the green parts of the stem behave differently from those 

 in the assimilating lamina of the leaf: this, according to my view, is also demon- 

 strated by the fact that during growth in the. dark, the otherwise green partS; 

 of the stem and petioles remain white, while the assimilating laminae appear yellow 

 in the etiolated state. Schimper found that in the stems of many plants the 

 starch-grains do not arise at any haphazard points of the chlorophyll-corpuscle, 

 but exclusively close beneath its surface, so that they soon protrude from its 

 substance. Hence the following distinction results. The grains which remain 

 entirely in the chlorophyll-corpuscle are rounded, and possess a concentrically layered 

 structure, because they are nourished on all sides from the chlorophyll; whereas, 

 the starch - grains growing out from the chlorophyll - corpuscl s are stratified 

 excentrically, since they grow much more strongly and exhibit more numerous 

 layers on the side connected with the chlorophyll — a proof that they are nourished 

 from this side. 



A long series of older inaccurate observations are rectified by Schimper's research, 

 in that the starch^grains so common in organs other thail the assimilating organs 

 — petioles, stems, subterranean tubers and roots, and young leaves which do not yet 

 assimilate^-are produced by peculiar little bodies which Schimper terms 'starch- 

 forming corpuscles ' or Amyloplasts {Siarkebildner). These starch-forming corpuscles 

 are protoplasmic, usually colourless structures, which become differentiated from the 

 protoplasm just like the chlorophyll-corpuscles themselves, either in the neighbour- 

 hood of the cell-nucleus, or also in the rest of the protoplasm. These starch-forming 

 corpuscles now produce starch-grains, either in the interior of their substance 

 {Colocasia and endosperm of Melandryum), or only at their peripheral portions 

 (Philodendron, Amomum, Phajtts, and Canna), and thus in the same way as the 

 assimilating chlorophyll-corpuscles in the leaves. The peripheral mode of origin 

 appears to predominate however in these non-assimilating starch-forming corpuscles. 

 According to Schimper's statements also the protoplasmic substance of the starch- 

 forming corpuscle is more quickly and essentially altered, or used up, during its 

 functional activity than is the case with the assimilating chlorophyll-corpuscles. The 

 similarity of the starch-forming corpuscles to the assimilating chlorophyll-cor- • 

 puscles is, however, still further increased, in that the former can in most cases 

 develope into chlorophyll-corpuscles under the influence of light. In this process, 

 they increase considerably in size, and, their starch-grains dissolving, they turn 

 green at the same time — a process long known, for example, in the cortex of 

 potato-tubers allowed to lie in the light for some time, but incorrectly explained. 



The great difference between the starch-forming corpuscles and the assimi- 

 lating chlorophyll-corpuscles, however, Is estabhshed by Schimper himself in the 

 following words — 'Etiolated plants which have not yet exhausted their stores of 

 reserve-materials contain, as is well known, no starch in the mesophyll of the leaf, 

 but often have abundance of it in their stems and petioles, and in the vascular 

 bundle-sheaths of their leaves. This starch, which of course can only be a product 

 of metastasis and not a product of assimilation formed there, is produced by 

 starch-forming corpuscles. Good examples of this are afforded by the leaves of 

 Hyactnthus, the stems of Begonia cucullata and Oxalis Ortgiesii, and the cortex 

 of the stem of Philodendron grandifolium. These starch-forming corpuscles 



