172 



KNOWLEDGE 



[August 1, 1895. 



the peptones into "nitrogenous crystalline bodies, ebiefly 

 amides, such as leucin and tyrosin"; steopsin, which 

 emulsifies fats, and then splits them up into glycerine and 

 fatty acids ; and amylopsin, by whose action starch is 

 converted into sugar. 



Now, it will be our endeavour to show that all these 

 ferments have their representatives in the plant-kingdom, 

 and to show what uses they subserve there. 



In the foregoing figure (Fig. 1) we have a section 

 of the maize fruit, cut so as to show the connection of the 

 nourishing matter, or endosperm, with the embryo-plant. 

 The endosperm is markedly divisible into two portions ; 

 that to the left, shaded darkly, consists of cells filled with 

 nitrogenous material, the cells of the lighter shaded part 

 adjoining the embryo being densely filled with starch. 

 Starch is insoluble in water, and so cannot diffuse through 

 the cell-walls. It is found that during the formation of 

 the endosperm a ferment is formed whose function appears 

 to be the conversion of starch into a substance that can 

 easily pass through the cell-walls, and so be directly 

 available as food for the growing embryo. This ferment 

 has received the name of diastase. It converts starch 

 into sugar. But diastase is not confined to the seeds of 

 certain plants. It is of very common occurrence in the 

 vegetable world. Indeed, one observer has asserted that 

 it is present in all living plant cells. We may take as an 

 instance the potato-tuber and show its use there. During 

 summer the chlorophyll-bearing cells of the potato-plant 

 manufacture a large quantity of sugar, much more than is 

 required for its own growth. The superfluous sugar is 

 carried down to the underground stem and is there stored 

 in the form of the non-diffusible starch in portions of the 

 stem, which in consequence become much swollen, forming 

 the potato-tubers. These remain dormant during winter, 

 but burst into vitality the following spring. Each eye, 

 which is in reality a bud, shoots out into a stem bearing 

 leaves, even although the tuber be kept in a dark cellar, 

 and one observes that at the same time the tuber 

 decreases in size and ultimately becomes quite shrivelled 

 up. The development of the stem thus takes place at the 

 expense of the tuber ; it is accompanied by complex chemical 

 changes, one of which is the conversion of the starch in the 

 tuber into sugar by the agency of the diastase stored up 

 there. The sugar thus formed helps to build up the proto- 

 plasm of the growing aerial stem. 



Numerous other instances might be cited of the presence 

 of this ferment in plant cells. In fact, its common 

 occurrence has led to the classification of ferments having 

 a similar action as diastatic ferments. It is obvious that 

 the ptyalin of the saliva is one of these. 



The action of diastase upon starch can be demonstrated 

 ia the following manner. The diastase is extracted from 

 the seed by means of water and glycerine, and poured into 

 a " solution " of starch. After a longer or shorter period 

 • — depending upon the temperature — the starch is seen to 

 be converted into sugar. If its action be examined ;'/( situ 

 it is noticeable that the grains are gradually dissolved in a 

 uniform manner. 



It has recently been shown by Brown and Morris that in 

 addition to the diastase, whose almost universal presence 

 in living plant cells we have just noted, there exists in the 

 seeds of certain grasses another form of diastase, to which 

 they have given the name of "secretion diastase" to 

 distinguish it from the former, called by them " trans- 

 location diastase." Referring to Fig. 1, we see that a 

 portion of the stem below the first leaf (cotyledon) is very 

 large and shield-shaped. On this account it has received 

 the name of scutellum. In its outer layer of cells, or 

 epithelium, adjoining the endosperm, the secretion diastase 



is manufactured, and it is poured forth into the neighbour- 

 ing endosperm cells, where its presence can be detected by 

 its remarkable action upon the starch grains. It converts 

 these into sugar, but their dissolution does not proceed 

 uniformly; instead, the grains assume "a markedly pitted 

 appearance, and ultimately dissolve. This diastase also 

 differs from translocation diastase in the time of its 

 appearance. It is only formed when the grain commences 

 to germinate. Its function thus appears to be the 

 conversion of starch into sugar for the benefit of the 

 germinating plant. If the actively growing embryo (Fig. 

 2, a) be placed on starch paste, with the scutellum resting on 



Fio. 2. — A. Germinating embryo of Maize, detached from eudo- 

 ?perm ; ewrf., scutelluin ; s.y., secondary roots ; p.^ primary stem; 

 p.r., primary root. B. Transverse section of Date seed (•stone"). 



the paste, the starch grains will display marks of corrosion, 

 due to contact of the secretion diastase secreted by its 

 epithelium. 



Yet another digestive action occurs in the endosperm of 

 grasses, according to Brown and Morris. Previous to the 

 dissolution of their starchy contents the cellulose cell 

 walls near the scutellum become soft and ultimately dis- 

 organized. This is accompanied with the appearance of 

 starch in the epithelial sscreting cells. The diffusible 

 substance formed from the cellulose is not known. Prob- 

 ably it is sugar, which, passing into these cells, becomes 

 stored up as starch. The ferment causing this action has 

 been isolated ; it is a proteid substance, and is secreted by 

 the epithelial cells of the scutellum. These cells thus 

 secrete two ferments, one to dissolve the cell walls of the 

 endosperm, and another to dissolve the starch grains thus 

 exposed. 



There are certain seeds in which the endosperm is 

 composed mainly of cellulose. This is markedly the case 

 in the date palm ( PJianix dnctijlifera ). Everyone is 

 familiar with the extremely hard nature of the date 

 " stone." This stone is the seed of the date. A trans- 

 verse section of it is shown in Fig. 'A, b. The embryo 

 occupies only a small portion of the seed ; the remainder 

 is filled with endosperm which has taken the form of 

 cellulose. An examination of the seed a short period after 



