THE CONVERSION OF THE PRODUCTS OF ASSIMILATION. I 149 



would be used up in equal proportions, as when germination takes place in 

 darkness and when the seedling is provided with distilled water only. In 

 nature, the root, as we have said, generally forces its way at once into the soil 

 and draws therefrom the necessary minerals, and since its duty is to supply 

 the seedling with such materials from the very first, naturally we need not 

 expect more than a trace of minerals in the seed itself. This is the reason why 

 GODLEWSKI (1879) found that seedlings of Raphanus developed far better in the 

 dark when he provided them with nutrient salts than when he gave them 

 distilled water only. It was only then that the seedlings could make full use 

 of the organic reserves and so attain twice the weight they reached when 

 grown in pure water. If excess of non-nitrogenous reserves be supplied and no 

 nitrates be given, or if these bodies cannot be assimilated sufficiently in the 

 dark, growth in the long run comes to a standstill. The converse is true of 

 many Leguminosae ; although development is inhibited in darkness, one still 

 finds in the seedlings nitrogenous organic substance accumulated in quantity 

 out of all proportion to the amount of non-nitrogenous substances present. 

 The degree of development is determined here also by the nutrient present 

 in minimum quantity (compare Lecture VII, p. 83). 



The reserves in seeds are bodies either entirely insoluble in water or charac- 

 terized by having very large molecules (colloids). This has two advantages ; 

 in the first place, substances containing no water take less room, and in the 

 second, the high osmotic activity of concentrated solutions of crystalloids is 

 avoided. We shall find that non-desiccated storehouses behave quite differ- 

 ently. The non-nitrogenous reserves which occur most commonly in seeds are 

 starch, cellulose, and fat, the nitrogenous bodies are represented by proteids. In 

 order to understand clearly how the dissolution and translocation of reserves 

 is effected it will be most convenient for us to begin with a consideration of 

 starch, for it is not only a very common reserve, but has also been the most 

 thoroughly studied. 



As already remarked, starch is insoluble in water unless chemically altered. 

 Such alterations as give rise to soluble products may be effected, apart from the 

 plant, in very various ways. Water at a high temperature acts in this way, 

 causing starch to turn first of all into a paste and finally altering it into dextrin 

 and dextrose. A similar decomposition is induced by mineral acids (e.g. hydro- 

 chloric acid), especially if these be warm. Other products are formed, however, 

 when starch is dissolved in alkalis, calcium nitrate, chloralhydrate, &c. In the 

 plant, starch, whether it be growing or whether it be dissolved, is surrounded by 

 the chromatophore and cannot come in contact either with acids or alkalis ; 

 its dissolution is effected in the plant by means of a substance with quite peculiar 

 properties, viz. diastase, belonging to the physiological group of enzymes 

 or ferments (compare SCHLEICHERT, 1893). Diastase is a product of the activity 

 of the organism, but is capable of carrying out its functions apart from it. The 

 most convenient method of obtaining diastase for study is to take some seeds 

 containing abundant starch, such as barley, a short time after the commence- 

 ment of germination, grind them down and extract them with water at a tem- 

 perature of about 50 C. The diastase and other soluble bodies dissolve in the 

 Water, and we thus obtain a barley or malt extract for purposes of investigation. 



On treating starch grains with this extract, we find that they gradually 

 dissolve in precisely the same way as they do in the uninjured germinating 

 seed (Fig. 32, p. 155). We may obtain a knowledge of the resulting products 

 more readily by investigating the alteration effected in starch paste. Employ- 

 ing the iodine test we find that the original blue reaction rapidly gives place 

 to a wine-red coloration. Finally, this latter reaction also disappears. Even 

 without using iodine the fluid exhibits a marked alteration in appearance. 

 Originally it is semi-fluid and opalescent ; now it becomes transparent and 

 quite watery. The starch, as such, has disappeared, and dextrin and maltose 



