THE CONVERSION OF THE PRODUCTS OF ASSIMILATION. II i6i 



general occurrence in nature ; in the plant world pepsins seem to be entirely 

 absent. Since, in the germination of seeds with abundant proteid, amino-acids, 

 or other similar substances produced by the action of the pancreatic secretion, 

 may be recognized, more especially if by cultivation in darkness an accumulation 

 of these bodies is induced (Lecture XIV), we may legitimately conclude the 

 presence of a trypsin-like enzyme in the germinating seed. A ferment of this 

 kind has been discovered by Green (1887) in lupins and Ricinus (1890), and by 

 Neumeister (1894) in barley, poppy, wheat, maize and rape. Neumeister, 

 however, searched in vain in many other seeds for a protease, although one 

 would have expected to find such enzymes most readily in seeds, such as those 

 of many Leguminosae (lupin, vetch, pea), containing large quantities of proteid. 

 BuTKEWiTSCH (1900) has fully confirmed Green's work on the lupin in 

 opposition to Neumeister's conclusions, and was able to show conclusively 

 that leucin and tyrosin were formed from proteids of Leguminosae by acting 

 on the latter with a glycerine extract of germinating seeds. Windisch 

 and ScHELLHORN (compare Green, 1901) have also discovered a trypsin-like 

 protease in germinating barley. There is thus nothing to prevent us assuming 

 the presence of proteases in all proteinaceous seedlings. [These have also been 

 found in unripe seeds by Zaleski (1905).] According to the observations of 

 Puriewitsch (1897), such an assumption is certainly not necessary in all cases. 

 Whilst only amido-compounds can be recognized in the culture fluid when 

 cotyledons of lupins empty themselves of their own accord, other seedlings 

 treated in a similar way give off into the surrounding fluid either amides in 

 addition to proteid or peptone, or peptone and proteid only. It must be 

 assumed from this that proteid as such can pass through the protoplasm and 

 cell-wall, a possibility which we have not hitherto generally taken into account, 

 but one which, especially after our experience of the ability of fats to penetrate 

 such walls, cannot be regarded as unlikely. 



In the decomposition of proteid, sulphates also are set free, as mentioned 

 on p. 139. The globoids give off phosphoric acid (compare Zaleski, 1902), which 

 may arise also from lecithin. Many seeds contain not inconsiderable quantities 

 of this organic compound, which contains phosphorus but no sulphur, and hence 

 in the process of germination much phosphoric acid may arise from this source. 

 [According to more recent investigations only a very small part of the phosphoric 

 acid arises from lecithin ; phytin (oxymethylphosphoric acid), on the other 

 hand, appears to be the most important source of this acid. (Compare 

 p. 145). (PosTERNAK, 1903 ; IwANOFF, 1902).] It is doubtful whether 

 phosphoric acid occurs in seeds in a less complex combination, e. g. as an in- 

 organic salt. The same may be said of other ash constituents ; calcium and 

 magnesium, and apparently iron also, are present in the globoids in organic 

 form, but perhaps they may occur in seeds in other forms as well. [Posternak 

 (1905) shows that all the essential materials of the ash are present in the aleurone 

 grain, potassium, silicon, and manganese, as well as those mentioned ; whether 

 they are all present in the globoid he does not say.] 



Reserve substances are by no means restricted to the storage tissues of 

 seeds, on the contrary they are found wherever individual cells or tissues occur 

 independently of special assimilatory activity. Next to seeds stand those organs 

 which subserve the purposes of reproduction and multiplication, viz. those end- 

 less types of structures which are known as spores and propagative buds, and 

 amongst these must be included the pollen-grains of the flowering plants. The 

 special significance of the reserves in all these cases lies in the fact that they 

 serve to support the new individual in its development until it has reached 

 independence and can live on the products of its own assimilatory activity, or 

 until it has fulfilled its function (pollen). In other cases, the reserves render 

 possible the formation of new vegetative organs in such plants as pass through 

 a resting period during which they rid themselves of all superfluous structures. 



