THE CONVERSION OF THE PRODUCTS OF ASSIMILATION, I 155 



abundant supply of this reserve (about 80 per cent, of the dry weight). Fig. 31 

 shows a longitudinal section through the lower end of a grain of wheat. Within 

 the testa, which is in this case fused with the wall of the fruit, we observe the 

 embryo {Em), well developed and possessing a special organ, the so-called 

 scutellum {Sc), lying against the abundant endosperm {End). The contents of 

 the cells of the endosperm are not homogeneous. A single layer of peripheral 

 cells (the aleurone layer, Al) containing aleurone grains, lies immediately within 

 the testa, while the large central mass is packed with starch. Diastase may be 

 demonstrated even in the resting endosperm, and it becomes very noticeable 

 when water is absorbed at the beginning of germination. It produces a disso- 

 lution of the starch which may become very extensive if the maltose which 

 arises in the process be removed. In normal germination this is effected by the 

 seedling absorbing greedily the sugar presented to it by means of the super- 

 ficial layer of the scutellum. If the embryo be removed, not only does the 

 translocation of the sugar come to an end, but its formation also ceases and the 

 starch grains remain intact. Hansteen (1894) and Puriewitsch (1897) were 

 able to show that an emptying of the endosperm cells took place in the absence 

 of an embryo, if the seed were placed in contact with a large quantity of water 



End 



"^'i'^^kft 



^^ 



"w^m^ 



Fig. 31. Longitudinal sec- 

 tion through the lower part of 

 a grain of wheat ; End, endo- 

 sperm, A/, aleurone layer, £m, 

 embryo, Sc, scutellum. After 

 Sachs (i862),slightly magnified. 



Fig;. 32. Starch grains from germinat- 

 ing Barley. 1-4, successive stages in the 

 dissolution of the grain. From the Bonn 

 Textbook. 



with due antiseptic precautions, in such a way that only a small part was sub- 

 merged. The experiment was so arranged that in place of the embryo a plug 

 of gypsum was applied to the endosperm where the scutellum had been, its 

 lower part being in contact with water. It was found in this way that various 

 grass seeds exhibited after about a week many corroded starch grains in the 

 endosperm (Fig. 32) ; after eight to fourteen days most of the cells were com- 

 pletely emptied, and a sugar, which was capable of reducing Fehling's solution, 

 could be demonstrated in the water which removed it from the endosperm. 

 Whether this sugar corresponded in amount to the starch which had disap- 

 peared seems not to have been determined, but obviously the determination of 

 this point is of great importance in coming to a decision on the question. 

 Further, a complete evacuation of the starch in Puriewitsch' s experiments 

 took a much longer time than in the case of the normal seedling. It is not 

 probable that the imperfect removal of the sugar formed was the cause of 

 this, although no other explanation is available at present. It has been 

 clearly proved (Linz, 1896) that the scutellum contains at any time more (or 

 more active) diastase than the endosperm, so that it may be that in normal 

 germination diastase from the scutellum penetrates the endosperm and there 

 assists in the dissolution of the starch. Although it cannot be doubted that 



