CONCLUSIONS RELATING TO THE STARCH-SUBSTANCE, ETC. 81 



in its early stage of development is, as has been shown, a spherical homogeneous mass, 

 hut there comes a time when (owing to changes in internal or external conditions) crystal- 

 lization occurs, during which there arise those conditions of tension which cause contrac- 

 tion changes of such a character as to form the hole or funnel-hke ca\'ity, etc., that we 

 understand as the hilum. In grains of many starches after the formation of the hilum 

 fissures form which tend to become more numerous and deeper as the grain approaches 

 full growth, particularly when it is subjected to drying. The grains of some species show 

 no evidence of fissuration upon drying, or even upon dehydration at 120 C, yet those of 

 other species, even while in the cell-fluid, are more or less markedly fissured. This shows, 

 of course, differences in the degrees of molecular tension, and it is not unhkely that these 

 differences are in close relationship to stereochemic differences in the starch-substance. 

 Since the young amorphous grains are, in comparison with the portions of the grains subse- 

 quently deposited, rich in phosphorus, we may have here an explanation, or at least an 

 expression, of conditions which may inhibit crystaUization in the young grain but permit of 

 crj'stallization at a certain stage of growth after the deposition of a less rich phosphorus- 

 bearing starch-substance upon this spherical nucleus wliich may lose some of its phosphorus. 

 The cause or causes of the lamellation are yet obscure, but there are no reasons for 

 beUe\ing that they are essentially different from those giving rise to the same phenomenon 

 in spherocrystals of other substances. The assumption that they are a result of an alter- 

 nation of light and darkness, or of ^'ariations in the concentration of solution, etc., has 

 been clearly disproved, for instance, by Fischer and St. Jentys. 



(4) The hypothesis of growth of the starch-grain by intussusception is, as Fischer 

 and others have shown, absolutely untenable; whereas the hypothesis of growth by external 

 accretion is entirely consistent with our knowledge of the structm-e and growth of other 

 crystalline structures and with the peculiarities of the starch-grain and the phenomena 

 observed in the starch-producing structures. 



(5) The form or shape of the starch-grain is not fortuitous, but definitely determined 

 primarily by specific characters of the starch-producing structures, which are differentiated 

 not only in different plants in ways more or less peculiar to the plant, but also even in 

 different parts of the same plant, or even in the same organ; and secondarily by various 

 incidental conditions, such, for instance, as the presence of protein and other crystalUne 

 structures within the starch-formers, and to some extent, in certain plants, by the mutual 

 pressure of grains in contact. 



(6) The production or synthesis of starch, excepting possibly in the lowest forms of 

 starch-producing plants, is due probably essentially or even solely to specialized starch- 

 producing protoplasmic structures, which may or may not contain chlorophyl; but the 

 presence of chlorophyl, even in the case in chlorophyllous plastids, is not essential to 

 starch formation by these plastids, as is shown in the fact that etiolated plastids may 

 produce starch. Chlorophyl may be and usually is entirely absent from the leucoplasts 

 of bulbs, tubers, conns, rliizomes, etc., which are very active starch-producers. In fact, 

 chlorophyl may be merely in the nature of an energizer. (See page 22 of the Hemoglobin 

 memoir refeiTed to in the Preface.) 



(7) The starch-grain is a spherocrystal having properties in common with sphero- 

 crystals of other substances, and hence having molecular properties in accord with those 

 of rectilinear crystals. There are not any facts to justify a belief of a special microscopic 

 form of structure of the starch-crystal, such as held by Niigeli's micellar theory or Meyer's 

 trichite theory, which distinguishes the starch-crystal from other spherocrystals. Starch- 

 crj'stals must have characteristics dependent upon intramolecular structure and intermolec- 

 ular arrangement which distinguish them from the crystals of other substances, and if the 

 starch-substance exists in a number of stereoisomeric forms, the properties of the crystals 

 will vary accordingly, because of molecular differences. 



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