STARCH. 



[ 731 ] 



STARCH. 



alone in the barren flovcers of the monoe- 

 cious and dicvcious genera. Stamens pre- 

 sent a great variety of interesting points for 

 examination under a simple microscope 

 with a knv power, in their forms, append- 

 ages, pores, itc. For the compound micro- 

 scope they aftbrd good material for the study 

 of development of cells in the pollen, the 

 POLLEN-grains themselves, and the spiral- 

 fibrous tissue of their anthers. 



STARCH or Amylfm. — This substance, 

 with the exception of the protoplasm, is the 

 most generally diffltsed 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 varymg 

 quantity, in all 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- 

 gi'ains 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 acqmre a more or less 

 definite form, diverging from the spherical, 

 and often characteristic of the particular 

 plant in which the gi'ain is pi'oduced. 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 Carina 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 ti'ansitory. 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 ceUuhjse structures of the cell- 

 wall through the remarkable secondary 

 layers foimd in the Axbi^men of certain 

 seeds, composed of the substance called 



served, more 

 cases, which 



ann/l<nd, 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 de\olopmeut. 



The structure of the starch-granule has 

 formed the subject of much debate, wliicli, 

 however, seems to have originated rather 

 through considerations relating to the deve- 

 lopment than from a difficulty in observing 

 the complete objects. Very minute granules, 

 as above stated, appear as solid globules ; 

 but when the granules acquire appreciable 

 dimensions, concentric lines may be ob- 

 or less distinctly in difterent 

 lines increase in number with 

 the increase of size, in many cases, however, 

 soon becoming exceutrical 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 Irispallida,Jioyentina, &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 

 starting-point of growth, solid or hollow as 

 the case may be, is sometimes called the 

 hihtm or the rincleus : 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 fimnel-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 gi'anule (PI. 40. 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 



