CONTENTS OF CELLS. 503 



many herbaceous Monocotyledonous stems, as that of the White Lily 

 (fig. 552), &c., by the appearance of single or several starch-granule's 

 in old chlorophyll-corpuscles, or in the substance of the bands of Spiro- 

 gyra (fig. 549), &c. Still more strikingly is it shown in the development 

 of the starch-granules which ultimately densely fill the outer cells of the 

 endosperm of Maize, where they are at first free from each other, im- 

 bedded in a collection of protoplasm filling the cell (fig. 553, a), and, as 

 they expand, come into contact and almost displace all the protoplasm, 

 which remains only as a reticulation of slender threads (fig. 553, o). A 

 similar reticulation of protoplasm -threads remains on the walls of the 

 cells of the Potato-tuber after its starch-granules are formed. 



The origin of the compound granules, in pairs, fours, or very many 

 compacted together into a mass, moulded together by mutual pressure on 

 their contiguous surfaces, is readily explicable, since we often find several 

 isolated nascent granules in one chlorophyll- or protoplasm-corpuscle : as 

 the granules increase in size they come into contact, but remain bound 

 together by the mass of protoplasm in which they lie. Such granules 

 (found in the corms of Crocus and Arum (fig. 553, 6), in the Oat, and more 

 or less abundantly in many other Monocotyledonous plants) are mostly 

 simply coherent, so that they may be separated by slight pressure. But 

 it is not uncommon to find twin granules enclosed by external layers 

 common to both (fig. 553, a). 



Relation to Chlorophyll. Starch-grains are almost universally present 

 in chlorophyll, from which, indeed, they are formed. This opinion differs 

 from that of Mohl, but is supported by the discoveries of Sachs and Gris, 

 the former of whom shows conclusively that the starch is developed from 

 the chlorophyll under the influence of light, especially in the yellow, red, 

 or orange rays : if light be excluded, no starch is formed, what is already 

 formed disappears, but starch is again formed when the chlorophyll is once 

 more subjected to the influence of light. Without chlorophyll no starch is 

 formed ; it may, however, be stored up in cells containing no chlorophyll, 

 but is brought there from the cells in which it is formed. 



Decay of Starch-grains. Starch is a temporary ingredient of 

 the cell-contents ; it is accumulated during active vegetation, and is 

 abundantly deposited in the tissues of many organs which remain 

 at rest during certain seasons. In the recommencement of growth 

 it is dissolved, in consequence of the formation of diastase (which 

 converts the insoluble starch into soluble dextrine), and the as- 

 similated substance is applied to the formation of permanent 

 structure. 



Starch-grains are disintegrated or dissolved, when growth is about to 

 take place, in two ways either locally (when the grains present a 

 worm-eaten appearance) or uniformly over the whole surface. 



Inulin. In certain plants starch-granules are absent in those 

 situations where they are generally abundant, being replaced by a 

 substance of analogous composition, called inuline. This has been 

 found especially in the roots of tubers of the Composite. It is 



