STARCH, 



[ 733 ] 



STARCH. 



in autumn, &c. The free granules occur 

 more particularly in the colourless organs 

 of plants in tubers, rhizomes, roots, and the 

 cambium region in the season of rest, in 

 the endosperm of ovules, or the ALBUMEN or 

 cotyledons of seeds, &c. The parenchyma- 

 tously grouped granules are found in the 

 albumen of seeds, especially of inaize and 

 rice. The comparison of the states and of 

 the course of development of the crowded 

 granules of maize throws much light upon 

 the manner in which starch-granules are 

 formed. 



In the first place, two rival doctrines exist 

 as to the order of development of the parts 

 of the granule. Most authors assert that 

 the granules grow by the superposition of 

 layers from within outwards, consequently 

 that the outermost layers are the youngest. 

 Other authors, especially Nageli, comparing 

 the granule to a cell, assert that the layers 

 are formed internally, the older ones ex- 

 panding to make room for them. There 

 can be no doubt that the first view is cor- 

 rect. In the next place a variety of notions 

 have been put forth as to the origin of the 

 starch-granule and its relation to the rest 

 of the contents of the cell, especially the 

 chlorophyll. It is curious to note the error 

 into which earlier observers fell from the 

 want of the guiding thread furnished by a 

 knowledge of the function of the proto- 

 plastic structures connected with the pri- 

 mordial utricle. The idea that the starch- 

 granule sprouted out from the cell-wall 

 corresponded with the original view of the 

 origin of the septum in cell-division ; while 

 the hypothesis that starch is developed from 

 chlorophyll, and the contrary notion that 

 starch-granules form the nuclei of chloro- 

 phyll-granules, both rest on actual pheno- 

 mena, in which, however, the chlorophyll 

 proper, that is the mere green colouring- 

 matter, bears no important share. 



The development of the starch-granule is 

 very beautifully illustrated in the gradual 

 ripening of the seeds of Maize j and in im- 

 perfect seeds, different parts of the same 

 grain often exhibit various stages of growth. 

 The tigs. 1 and 3 of PI. 4(3, show the gradual 

 formation of the starch-granules by depo- 

 sition from the internal surface of vacuoles 

 in the protoplasm filling the cell, exactly in 

 the same way as the primordial utricle 

 secretes cellulose layers upon its outer sur- 

 face. Fig. 28 shows minute starch-granules 

 originating in the same way in the proto- 

 plasm-current connected with the nucleus 



in the white lily ; and Criiger, who first 

 published this view in a decided form, has 

 shown that the large granules, with an ex- 

 centric hilum, originate in a similar position, 

 and owe the excentricity of their form to 

 the fact of their remaining imbedded at the 

 thicker end in the protoplasmic threads of 

 the primordial utricle, while the small free 

 end is gradually pushed out further from 

 the nutrient mass. The existence of starch- 

 granules in chlorophyll-masses is thus clearly 

 enough accounted for, now that we know 

 the chlorophyll-globules to consist of masses 

 of protoplasm coloured green by^ the presence 

 of an extremely small quantity of a sub- 

 stance acquiring a green colour under the 

 influence of light. Starch originates in 

 vacuoles in this as in any other protoplasm. 

 The groups of granules are formed through 

 the simultaneous origin of a number, in 

 vacuoles excavated in one large globule of 

 chlorophyll or colourless protoplasm. We 

 have tracedthis in the fronds of the Hepaticse. 

 It remains to speak of the diversities of 

 form and size of the large and perfect gra- 

 nules in different plants. A glance at 

 Plate 46 will give some idea of these, and 

 an inspection of the individual figures will 

 show how remarkably the characteristic 

 forms may vary in ne'arly related nlants, 

 even genera of the same family, as is the 

 case with the ordinary Cereal grains. Thus 

 in Maize (figs. 1,3,5), where the small grains 

 are, as usual, originally roundish or oval 

 (fig. 5*), they gradually press upon one an- 

 other and become polygonal in the cells of 

 the centre of the grain, where they are less 

 densely packed, remaining with obtuse edges 

 and angles (fig. 6), in the cells of the horny 

 outer part of the grain, where they adhere 

 more or less firmly together, forming an- 

 gular parenchymatous masses (fig. 3). The 

 central cavity is large here. In the grain 

 of Wheat we find delicate, transparent, len- 

 ticular granules (fig. 8), the striae faint ; in 

 Barley (fig. 9) they are more irregularly 

 discoid, with a thickened edge, the striae 

 obscure j while in the Oat (fig. 10) the 

 granules are of very small size, but of angular 

 forms and packed together in large numbers, 

 so as to form roundish masses with a smooth 

 surface, which readily break down into their 

 components when pressed ; the separate seg- 

 ments all exhibit their separate black crosses 

 in polarized light. In Rice (fig. 12) we find 

 somewhat similar conditions to those in 

 Maize ; but the granules are much smaller 

 and more firmly united, whence the gritty 



