CHAPTER II. 



METHODS USED IN THE STUDY OF STARCHES. 



The methods used in the preceding research (l'ul)U- 

 N. 173) were at iU inception suiltcicuUy satis- 

 ry to meet the theoretical requirement* of a purely 

 iry and exploratory investigation, but at the 

 work progressed it was found, as was to be expected, 

 that radical improvement* could be made in various 

 Advantage has been taken of this experience, 

 and while the me-tlnnls continue to be inexact, in the 

 conventional sense, they are practically exact so far as 

 satisfactory differentiation and recognition of different 

 tan-he* are concerned. For obvious reasons the descrip- 

 tions of the methods given in the previous research are 

 a in a large measure repeated, with some omissions, 

 ni.*litirttti"ii. unit addition*. 



1. PREPARATION or THE STARCHES. 



The starches were prepared from bulbs, tubers, rhi- 

 somes, bulbils, and pseudobullxi, all in the resting state, 

 metis were comminuted by the aid of an ordi- 

 nary culinary grater. Four or five volumes of water arc 

 added to the pulp, the mass strained through four thick- 

 nesses of cheese-cloth, and the pulp then washed with 

 sufficient water and strained as before. The starch-water 

 preparation is decanted in cylinders and the starch is 

 clean.-od l>\ repeated washing and deoantation. Finally 

 the starch is collected in shallow dishes, the water as far 

 as possible drained off, and the preparation dried at 

 a temperature of 50 C. By this simple means starches 

 ran be prepared which are with rare exceptions practi- 

 cally free from gross impurities. To have carried out 

 purification to the extent of practical demoralization 

 would have proven of far greater disadvantage than gain. 



MI i.TAXEOfB STUDIES OF STARCHES OF THE 

 PARENTS AND HYBRID AND OF THE MEMBERS 

 OF A GE 



For obvious reasons, in a comparative investigation 

 such as the present it is desirable to make simultaneous 

 examinations of all three or four starches of a set by 

 one of the various methods of study and to take up the 

 methods seriatim in preference to taking one starch 

 and subjecting it to the entire series of methods before 

 undying another specimen; the same plan commends 

 itself when there is a number of sets belonging to the 

 same genus. 



3. HISTOLOOIC METHOD. 



This method has been found to be of signal useful- 

 ness, and up to recent years it has been the sole reliance 

 in attempts to determine the kind of starch. It was, 

 however, perfectly obvious at the very inception of these 

 researches, and rendered dear as far back as the investi- 



gation of C. Nageli in 1858, that this method, unless 

 associated with others, could not be depended upon, and 

 that it was liable to be absolutely misleading. Moreover, 

 differences in form may not in the leut imply differences 

 in the starch-substance, as has been pointed out in early 

 chapters of the preceding memoir. Magnification rang- 

 ing from 85 to 400, sometimes higher, was used, accord- 

 ing to the size of the grains and incidental conditions. 

 A sufficient amount of dried starch was disseminated on a 

 slide and mounted in a very dilute Lugol's solution, care 

 being taken not to add a larger quantity of iodine than 

 is sufficient to accentuate the lamella*. Since starches 

 of different sources dhow wide differences in the intensity 

 with which they become colored with iodine, it was found 

 convenient to have on hand a number of solutions rang- 

 ing from 1 to 2 per cent down. By the aid of such onli 

 nary microscopic technique there were recorded the 

 form and size of the grain ; the position and fonn of the 

 h: 1 11 m ; the form, number, and other characteristics of 

 the lamella*; the characteristics pertaining to the form 

 f the grains, whether single or in doublets, triplets, 

 aggregates, etc. In describing the grains the terms 

 " proximal end " and " distal end " have been adopted, 

 the former being the end nearer which the hilum is 

 located. The " longitudinal axis " corresponds with an 

 imaginary line, extending from the proximal end through 

 the hilum to the distal end. In different starches and 

 in different grains of the same kind of starch this may 

 he the long or the short axis. The measurements of 

 eccentricity of the hilum have reference to the distance of 

 the hilum from the proximal end of the longitudinal axis. 



4. PHOTOMICROGRAPH ic RECORDS. 



Verbal descriptions of the histological characteristics 

 of starch-grains fail to convey adequate conceptions. 

 The notes included in the text have therefore been accom- 

 panied by photomicrographs of the grains lightly colored 

 with iodine, as seen in the microscope. In making these 

 photographs we used an ordinary Bausch and Lomb 

 microscope with a %-inch objective and a 2-inch eye- 

 piece, which gave us a magnification on the field of 

 projection of 300 diameters. For obvious reasons, many 

 of the more minute features of the grains will not be 

 seen in the photomicrographs. Moreover, inasmuch as no 

 two fields are alike in case of any starch or slide, the 

 pictures are to be taken as being grossly of an average 

 character of a field. In recording the histological de- 

 scriptions, especially as regards variations in form, many 

 fields were examined. 



The photomicrographs of the plant tissues were 

 made by the use of a IV^-inch objective and a 2-inch 

 eye-piece (draw-tube in), or a %-inch objective and a 



