60 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



process of the saccharification of starches with mineral acids or with diastase the iodine 

 reaction shows all the changes of color which may be observed in the intact grain, as well 

 as of starch-paste under certain conditions, it may be assumed that tliis process (contrary 

 to the universally accepted view of the progressive formation of the dextrins) depends 

 upon the splitting up of the compounds of sugar and various tamiins in the form of glu- 

 cosides, and to the successive decomposition of separated or free tannins. St. Jentys 

 believes that numerous observations seem to support this theory. For instance, starch- 

 paste which had been colored blue with iodine on being treated with powdered leather, 

 first turned violet and then became colorless, and it had the property of reducing Fehling's 

 solution. On distilling acidified starch-paste with sulphuric acid in order to test for sugar, 

 an aromatic volatile body with a peculiar, unpleasant odor went into the distillate, which 

 combined with iodine without a color reaction. 



OCCURRENCE OF THE STARCH-GRAIN IN PLANT LIFE. 



C. Nageli (loc. cit.) gave careful study to this subject, and this section is a free trans- 

 lation from his memoir. He states that starch has a very general distribution throughout 

 the vegetable kingdom, but that it is absent from the Fungi, Diatomacece, ChroococcacecE, 

 Nostocaceoe, and many other cellular plants, and also apparently from some vascular Pteri- 

 dophyta. Little or no starch is found in colorless parts of plants of one year's growth from 

 which no new structures arise, but on the other hand more or less starch will always be 

 found in tissue containing chlorophyl. The vegetative parts which develop organs often 

 store up considerable amounts of starch in their colorless portions when they are not too 

 near the surface and are of the right age, for example, the miderground parts of perennial 

 herbaceous plants, all of which contain a great deal of nutritive material, and from which 

 starch is seldom wholly absent. Furthermore, the stems and branches, also portions of 

 the roots of trees and shrubs, contain starch, which is present in the pith, in the medullary 

 rays, and in the wood-cells up to a certain age of these organs, generally in small quan- 

 tities, or occasionally in considerable quantities, in the region near the leaves. Finally, it 

 is observed in the pith of this year's sprouts, in the receptacle, and even in the placenta. 



In seeds the presence or the absence of starch-grains is more sharply defined than 

 in other portions of the plant which contain nutrient material. Generally all of the genera 

 of one order correspond in this respect, this holding good for eleven-twelfths of the natm-al 

 families; and the genera of the same order are seldom dissimilar in this particular, and still 

 more rarely the species of a genus. No starch-grains occur in the seeds of about four-fifths 

 of the natiu-al families and about nine-tenths of all the genera of Phanerogams. Starch is 

 present in the seeds of about half of the families and genera of Gymnospermce and Mono- 

 colyledones, while it is absent from the other half. Starch is found in the seeds of about 

 one-sLxth of the Dicotyledones, and in only one-fourteenth of the famiUes and in a still 

 smaller fraction of the genera of Gamopetalce. 



When starch-grains are present in seeds, other reserve foods are almost entirely 

 excluded; if seeds which are rich in starch have perisperm, then the embryo with few 

 exceptions contains oil and no starch-grains ; but if perisperm is absent from the seeds, the 

 starch is found in the cotyledons, while only oil is usually present in the cells of the canicle 

 and plumules. Whenever the various genera of an order differ in this respect, it will occur 

 usually among those which have seeds of different sizes, starch being found in the large 

 seeds and lacking in the small seeds. The resting spores of Cryptogams usually have no 

 starch-grains, but if two kinds of resting spores are present they usually agree in that starch 

 is in both either present or entirely absent. Starch is absent in the majority of the pollen 

 grains of Phanerogams. 



If we consider the development of the entire plant, the formation of starch always 

 occurs in the tissues at certain stages of their growth and disappears from them at a definite 



