SPECIAL CASES 599 



diastase may be regulated according to the needs of the plant. The 

 disappearance of starch from the scutellum inwards affords no certain 

 proof that the latter excretes diastase, for the same phenomenon is shown 

 when the isolated endosperm is emptied by contact with water 1 , and if 

 the back of the endosperm is exposed to contact with water the disap- 

 pearance of starch progresses from this surface inwards. The fact that 

 fragments of living endosperm may be partially or entirely emptied in 

 a similar manner shows that all cells of the endosperm possess more or 

 less marked mobilizing powers, and also disproves Haberlandt's 2 supposition 

 that the aleurone layer is responsible for the production of diastase. The 

 changes produced can hardly be due to diastase alone, for not only reducing 

 sugar but also a non-reducing sugar (probably cane-sugar) appear as the 

 products of mobilization. No enzymatic action is necessary in the seeds of 

 grasses for the removal of their nitrogenous reserves, for according to 

 Puriewitsch these appear in the surrounding fluid mainly in the form of 

 pi'oteids. It is however possible that in certain cases the aid of proteolytic 

 ferments may be invoked. 



The absorbent parts of the cotyledons seem to have a more or less 

 marked power of producing and excreting diastatic and cytasic or cellulose- 

 dissolving ferments. This is especially the case when insoluble carbohydrates 

 are stored in the seed, for a cellulose ferment has commonly been detected 

 in seeds which contain reserve-cellulose. The latter may, however, also be 

 mobilized by the storage-cells themselves, for Hansteen found that in time 

 the isolated mucilaginous endosperm of Tetragonolobus purpurcns might be 

 almost entirely emptied by continually removing the sugar produced, while 

 Puriewitsch has shown that the same occurs in the isolated endosperm 

 of Phoenix dactylifera when kept in contact with a continually renewed 

 supply of water 3 . 



Similarly the starch disappears from the isolated cotyledons of Pisum 

 sativum, Vicia faba, Phaseolus multiflorus (Puriewitsch), if the sugar pro- 

 duced is continually removed, and oil disappears from the isolated 

 cotyledons of Ltipinus albus (Puriewitsch) and Helianthus animus (Hansteen) 

 in the same manner when they are kept in contact with water. Moreover 



1 The progress of the metamorphosis may be different when the mobilized products exercise no 

 marked inhibitory action. Van Tieghem (1. c., p. 186) states that the changes commence peripherally, 

 and rapidly spread over the entire albumen. Sachs (Sitzungsb. d. Wien. Akad., 1859, Bd. xxxvn, 

 p. 90) observed that in the scarlet-runner the convergipn of starch begins at the stalk of the cotyledc 

 and travels outwards, whereas Baranetzsky (Die itrkeumbildenden Fermente, 1878, p. 58) found 

 that in other cases the solution of starch progressed centripetally. 



a Haberlandt, Ber. d. Bot. Ges., 1890, p. 46. 



3 On the different forms of reserve-cellulose, cf. Sect. 83. On the mode of deposition and 

 process of solution: Griiss, Landw. Jahrb., 1896, Bd. XXV, p. 386; Bibl. hot, 1896, Heft 39 .; 

 E. Schulze, Ber. d. Bot. Ges., 1896, p. 66 ; Elfert, Bibl. hot., 1894, Heft 30; Nadelmann, Jahrb. f. 

 wiss. Bot., 1890, Bd. xxi, p. 609; Reiss, Landw. Jahrb., 1889, Bd. xix; Leclerc du Sablon, Rev. 

 gen. d. Bot., 1895, T. vn, p. 401 ; Coley, Bot. Centralbl., 1897, Bd. LXX, p. 204. 



