10 



THE AMERICAN MONTHLY 



[January, 



to even briefly consider the relations 

 between starch and chlorophyll, as 

 this part of the subject is still envel- 

 oped in uncertainty. Some observers 

 consider that starch is the direct pro- 

 duct of the action of light upon 

 chlorophyll, while others deny that 

 chloroplwll is necessary for the pro- 

 duction of starch. The granules orig- 

 inate in vacuoles in the protoplasm of 

 plant-cells, and seem to be secreted 

 from the interior surface of the vacu- 

 oles, precisely as the cell-wall is de- 

 posited by the primordial utricle. 



Before considering this process 

 more particularly, it may be well to 

 allude to the structure of the perfect 

 granules. We are accustomed to say- 

 ing that starch is colored blue by 

 iodine, but the granule is composed 

 of two substances, only one of which, 

 known as granulose, is colored blue 

 by the iodine ; the other component, 

 cellulose, being quite inert. The 

 granulose is soluble in saliva, and in 

 dilute chromic acid. By treating the 

 granules with either of these re-agents 

 the soluble portion can be removed, 

 leaving the cellulose, and showing the 

 concentric markings of the granules 

 very distinctly. 



The hilum, or dark spot, to be seen 

 on almost all starch grains, was for- 

 merly regarded as the point of attach- 

 ment of the granules to the cell-wall. 

 It cannot be so considered at present. 

 It is merely ihe point at which growth 

 begun. The markings are usually 

 more or less eccentric, owing to the 

 more rapid growth of the granule away 

 ftom the protoplasm in which one end 

 is imbedded. 



The eccentric markings have been 

 supposed to indicate successive folds 

 in a membrane covering the granules, 

 but at the present time the views of 

 either Nageli or Strasburger are re- 

 garded as more probable. The for- 

 mer considers that the granules grow 

 by a process of internal growth, the 

 new material being added within, the 

 outer portions being the older. In 

 some way the granules become differ- 

 entiated into successive, enveloping, 



alternately firm and watery layers, 

 which cause the peculiar markings 

 seen on the surface. As the granules 

 increase in size the outer portions be- 

 come stretched or distended by the 

 accumulation of starchy matter within. 

 The evidence to support this view is 

 mainly founded upon observation of 

 the distension and destruction of the 

 granules by means of heat and chem- 

 icals. In warm water the successive 

 layers can be observed to separate 

 slightly, perhaps owing to the expul- 

 sion of air from between them ; and 

 this affords positive evidence that the 

 markings do not indicate folds of a 

 membrane. In boiling water the cells 

 swell very much, and some of them 

 burst, discharging a flocculent sub- 

 stance from their interior. Rather 

 strong sulphuric acid acts quite rapidly 

 upon the inner portions of the gran- 

 ules, at first causing them to expand 

 and distend the outer layers, but after- 

 ward the entire granule expands into 

 a very large, smooth sac. 



Strasburger's conclusions differ very 

 much from those of Nageli. He re- 

 gards the granules as composed of 

 concentric layers successively depos- 

 ited. 



According to this observer, if Na- 

 geli's view of the micellar structure 

 of organic bodies were correct, the 

 disintegration of a granule would not 

 affect the action of the particles upon 

 polarized light. The parts would still 

 act upon the light just as would the 

 parts of a double refracting crystal. 



Strasburger considers that starch 

 grains, and organic structures which 

 act upon polarized light, do so by vir- 

 tue of their organization as a whole — 

 of the arrangement of the ultimate 

 molecules composing them. In this 

 case, the moment the structure is de- 

 stroyed the polarizing action would 

 be lost. He regards the molecules of 

 all organic bodies as linked together 

 by chemical attraction in a reticulate 

 manner, probably by what are known 

 to chemists as multivalent atoms. Pro- 

 toplasm differs from other organized 

 matter because the molecules compos- 



