STARCH. 



[ 731 ] 



STARCH. 



alone in the barren flowers of the monoe- 

 cious and dioecious genera. Stamens pre- 

 sent a great variety of interesting points for 

 examination under a simple microscope 

 with a low power, in their forms, append- 

 ages, pores, &c. For the compound micro- 

 scope they afford good material for the study 

 of development of cells in the pollen, the 

 POLLEX-grains themselves, and the spiral- 

 fibrous tissue of their ANTHERS. 



STARCH or AMYLUM. This substance, 

 with the exception of the protoplasm, is the 

 most generally diffused of all the products 

 met with in the interior of vegetable cells, 

 and occurs in the form of transparent gra- 

 nules, of varied size and form and in varying 

 quantity, in ;;11 classes of plants but the 

 Fungi. * It has been stated that it sometimes 

 exists in a diffused or formless condition ; 

 but this seems questionable. All starch - 

 grains appear when newly formed as mi- 

 nute spherical bodies, and very many never 

 advance beyond this stage ; but a consider- 

 able proportion of the grains, in all cases 

 where the starch becomes an important and 

 considerable element in the cell-contents, 

 increase in size, and acquire a more or less 

 definite form, diverging from the spherical, 

 and often characteristic of the particular 

 plant in which the grain is produced. The 

 grains in a single cell mostly vary very 

 much in size, on account of their different 

 degrees of development ; but the full-grown 

 characteristic grains of the same species of 

 plant agree tolerably well in size. One of 

 the most remarkable peculiarities of starch 

 is the fact that it assumes a blue colour 

 when iodine is applied to it, which in most 

 cases affords a ready means of detecting its 

 presence. The smallest grains are almost 

 too minute to measure, and even their de- 

 termination by the application of iodine is 

 sometimes unsatisfactory; the largest grains, 

 such as those of Canna and the potato, for 

 example, attain a length of more than 

 1-400". 



The starch-granule is a definitely organ- 

 ized structure, although its existence in 

 relation to that of the cell is transitory. It 

 consists of assimilated food, deposited in a 

 definite form insoluble in the ordinary cell- 

 sap, through a process of organization ana- 

 logous to that by which the development of 

 the cell itself is effected. It is related 

 closely to the cellulose structures of the cell- 

 wall through the remarkable secondary 

 layers found in the ALBUMEN of certain 

 seeds, composed of the substance called 



amyloid, which sometimes takes a blue 

 colour when iodine is applied to it, and, 

 like starch, is ultimately dissolved and re- 

 moved to furnish material for development. 

 The structure of the starch-granule has 

 formed the subject of much debate, which, 

 however, seems to have originated rather 

 through considerations relating to the deve- 



but when the granules acquire appreciable 

 dimensions, concentric lines may be ob- 

 served, more or less distinctly in different 

 cases, which lines increase in number with 

 the increase of size, in many cases, however, 

 soon becoming excentrical from the pre- 

 ponderating growth of one side of the 

 granule. In freshly extracted granules the 

 original centre usually appears solid or with 

 a minute black point ; but if the starch is 

 dry, the centre appears hollow, sometimes 

 is even occupied by air; and some starch- 

 grains, as in 3ris pallida,jlorentina, &c., have 

 a large cavity. If strong alcohol is applied 

 to fresh grains, the abstraction of water 

 likewise produces a hollow in the central 

 point of growth ; and in all these cases, 

 cracks not unfrequently run out towards 

 the surface. The point in question, the 

 startkg-point of growth, solid or hollow as 

 the case may be, is sometimes called the 

 hilwn or the nucleus : the former term arose 

 out of the mistaken hypothesis of its being 

 a point of attachment to the cell-wall ; the 

 latter term is admissible in a general sense 

 as merely indicative of its precedence in age 

 of the general mass of the grain. It is 

 sometimes asserted that this point or nucleus 

 is a pore or funnel-shaped cavity ; but this 

 is altogether a mistake, as may be readily 

 proved by gently roasting a few starch- 

 granules of the potato on a slide, and ob- 

 serving how the expanding air blows up 

 the dextrine, into which the starch is 

 changed, in the form of a bubble or bladder. 

 Sometimes small granules occur in the 

 potato with a large cavity and thin walls. 



The lines seen in the starch -granules are 

 the boundaries of superimposed layers of its 

 substance ; sometimes these are 'very di- 

 stinct, sometimes very faint. Often more 

 distinct lines appear at intervals in the 

 series of the same granule (PI. 46. fig. 31); 

 and in these cases even a thin vacancy, or 

 in the dried granules a stratum of air, seems 

 to exist between the layers. The markings 

 have been described as " folds " on the 



