20 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



the fluctuations of light, so that the deposition by daj' is of a different density from that 

 by night. Fritsclie studied the grains from a number of plants and recorded results which 

 in general coincide with those noted in the studies with potato starch. (See pages 64 and 

 80 for other references to this author's work.) The view advanced by Fritsche of the 

 mechanism of the growth of the starch-grain was accepted, generally in more or less modi- 

 fied form, by a number of subsequent investigators, but opposed by others. 



The formation of the starch-grain by the deposition of the outermost upon the inner- 

 most layers was also held by Mulder (The Chemistry of Vegetable and Animal Physiology, 

 1838, 209), who states that starch-grains are formed from the sap and that their antecedents 

 exist first in a hquid state. Hence it follows, he holds, that the germ or nucleus of the 

 starch-grain must primarily be spherical and float freely in a liquid, from which elements 

 in solution are deposited in the form of lamellte upon that which is already solidified. 

 Each grain he conceives to be fixed to the walls of the inclosing cell by the hilum, the 

 real use of which, he states, is not known. The more freely, therefore, the germ or grain 

 floats about the more it should grow, and this he believes is really the case, since he found 

 that plants which are rich in sap contain larger grains than those which are not. The 

 starch-grains are, he believes, coated with coagulated albumin. 



JMiinter (Botanische Zeitung, 1845, iii, 193), from studies of the starch of Gloriosa 

 supcrba, ad\'anced a view opposite to that of Fritsche and Mulder as to the mechanism 

 of formation of the grains. He states that we know certainly that the concentric 

 contour, as, for example, in the so-called stone-cells of pears, is due to centripetal lamella- 

 tion. There is, therefore, nothing in opposition to the view that the layers of the starch- 

 grain originate by centripetal deposition. Tliis theory, he holds, is strengthened by the 

 fact that the hilum is watery or gelatinous. "WTien sulphuric acid is applied to the grain, 

 water is extracted, and the hilum is replaced bj^ an air-bladder. The same phenomenon 

 takes place when the grain is heated, and even when fresh starch is dried at ordinary 

 temperature. This he assumes explains the formation of cracks in dried starch in the 

 region of the hilum. Since the hilum and the layers nearest it are richer in water than 

 the outer layers, causing the inner layers to be softer and less consolidated, one must 

 conclude that the hilum and the surrounding layers were last formed, and that, according 

 as the layers are thick or thin, the hilum must lie more and more eccentrically. 



The fii'st mention of cliloroplasts was made by Unger in 184G (quoted by Schimper; 

 references on pages 30 to 33). 



Meyen (Zeitsclu*. f. wiss. Bot. 1847, 117) describes the starch-grain as a small bladder- 

 shaped structure containing condensed layers of starch. A similar view was expressed 

 by Kiitzing (Grundlaye d. philo. Bot. 1847, i, 263). 



Reissek (Flora, oder allegemeine botanische Zeitung, 1847, 13) from a study of normal 

 starch, and of the metamorphoses such as are seen when the grains lie in water for some 

 time, regarded the grains as undeveloped cells. ]\Iost starch-grains, he writes, in conse- 

 quence of the solution and exosmosis of the inner substance, become hollow and are filled 

 with water, and increase in size to such an extent that of the entire grain only the outer- 

 most layer remains. Since tliis layer becomes soft and tenacious, the changed grain assumes 

 the form of a small closed bag, and in such a form it represents a cell. In certain plants 

 starch-grains are formed which he believes may with certaintj^ be recognized as cells, as, for 

 instance, in the pseudo-bulbs of orchids. Here he states the outermost laj^er becomes differ- 

 entiated as a membrane and the internal filling mass is gelatinous, and that if one examines 

 the entire series of starch-grains from the various plants kno\An to us, there will be found all 

 transitional forms, from the simple homogeneous dense grains to the grains whose outer 

 substance has been diflferentiated into a membrane, and thus formed into a definite cell. 



Studies were made by Schleiden (Principles of Scientific Botany, 1849, 11) of the 

 normal starch-grain and of the effects of heating both dry and wet starch. He states that 



