STARCH. 



[ 612 ] 



STARCH. 



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 expand- 

 ing pari passu to make room for them. 

 There can be no doubt but that the first view 

 is correct. 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 protoplas- 

 mic structures connected with the primordial 

 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 chlorophyll-granules, both 

 rest on actual phenomena, in which, how- 

 ever, the chlorophyll proper, that is, the 

 mere green colouring matter, bears no im- 

 portant share. 



The development of the starch-granule is 

 very beautifully illustrated in the gradual 

 ripening of the seeds of Maize, and in imper- 

 fect seeds different parts of the same grain 

 often afford various stages of growth. The 

 figs. 1-4 of PI. 36, show the gradual forma- 

 tion of the starch-granules by deposition 

 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 surface. Fig. 

 20 shows minute starch-granules originating 

 in the same way in the protoplasm-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 excentric " hilum," 

 originate in a similar position, and owe the 

 excentricity of their form to the fact of their 

 remaining imbedded at one (the thicker) end 

 in the protoplasmic threads of the primor- 

 dial utricle, while the small free end is gra- 

 dually 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 chlo- 

 rophyll-globules to be really protoplasmic 

 structures 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 va- 

 cuoles in this as in any other protoplasm. 

 The groups of granules are formed through 

 the simultaneous origin of a number, in va- 

 cuoles excavated in one large globule of chlo- 

 rophyll or colourless protoplasm. We have 

 traced this in the fronds of the Hepaticacese. 

 These brief remarks must suffice on this part 

 of the subject, and further details must be 

 sought in the very copious literature which 

 exists. 



It remains to speak of the diversities of 

 form of the large and perfect granules in 

 different plants. A glance at Plate 36 will 

 give some idea of these, and an inspection of 

 the individual figures will show how remark- 

 ably the characteristic forms may vary in 

 nearly related plants, even genera of the 

 same family, as is the case with the ordinary 

 Cereal grains. Thus in Maize (figs. 1 to 6), 

 where the small grains are, as usual, origin- 

 ally roundish or oval (fig. 6), they gradually 

 press upon one another and become poly- 

 gonal; in the cells of the centre of the grain, 

 where they are less densely packed, remain- 

 ing with obtuse edges and angles (fig. 5), in 

 the cells of the horny outer part of the grain, 

 where they adhere more or lessfirmly together, 

 forming angular parenchymatous masses (fig. 

 3). The central cavity is large here. In the 

 grain of Wheat we find delicate, transparent, 

 lenticular granules (fig. 8), the striae faint ; 

 in Barley they are irregularly discoid, with a 

 thickened edge, the striae obscure ; while in 

 the Oat (fig. 10) the granules are of very 

 small size, but of angular forms and com- 

 pacted together in large numbers, so as to 

 form roundish masses with a smooth surface, 

 which readily break down into the com- 

 ponents when pressed ; the separate segments 

 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 

 character of rice-flour. In the Potato the 

 starch-granules are found larger (fig. 21) 

 than any of the above ; they are numerous 

 and loosely packed in the cells (fig. 20). 

 Among the more remarkable forms of starch 

 are the large grains of the Canute (fig. 25), 

 Musa (fig. 24), and most of the Zingiberacea3 

 (fig. 19). True East Indian Arrow-root (fig. 

 18) has compound grains of large size (mostly 

 detached in the prepared farina). Various 

 other kinds are illustrated in Plate 36. 

 Diejfenbachia Seguina (Aracese) has remark- 

 able lobed granules. 



