SPECIAL ADAPTATIONS 



375 



Similarly an excretion of acid enables certain fungal hyphae to perforate 

 egg-shells. 



Diastatic ferments are very widely distributed, and it is evident that 

 a mould or bacterium can only grow upon starch when it is able to convert 

 the latter into some soluble product. Similarly reserve-cellulose may be 

 rendered available for use in seeds by means of a cellulose-dissolving 

 enzyme, while the same occurs in the fungi which grow upon wood and 

 in the bacteria which decompose cellulose. Moreover glucose-yeasts can 

 grow upon cane-sugar when they are able to invert it, and many fungi also 

 have the power of producing invertase. 



Solid proteids can be absorbed only after they have been rendered 

 soluble by means of proteolytic enzymes, and these are actually excreted 

 by many carnivorous plants ; the liquefaction of gelatine by many bacteria 

 and certain fungi (Penicillium glanaim^ Aspergillus niger] shows that they 

 also can excrete a proteolytic ferment *. 



This term, however, and that of ' diastase-' as well, includes a variety 

 of different substances ; bacteria usually produce a tryptic ferment which 

 is active in an alkaline solution, whereas in carnivorous plants and the 

 above-mentioned fungi a peptic ferment is formed which acts only in an 

 acid solution. Many fungi and bacteria are even able to decompose 

 glucosides and fats. 



Various fungi (Aspergillus niger^ Pcnicillium glaucuvi) can perform all 

 these fermentative decompositions, but other plants have more limited 

 powers. Thus Drosera and Dionaea can excrete a peptic ferment only, 

 whereas in other cases (fungi and certain embryos) not only diastase but 

 also proteolytic enzymes are absent. The action of a particular enzyme is 

 strictly limited, but under certain circumstances a plant may secrete several 

 ferments simultaneously. A similar result may also be produced by the 

 co-operation of two different organisms, as, for example, when the diastatic 

 action of a fungus growing on starch renders a certain amount of sugar 

 available for other organisms. 



The production and excretion of enzymes exhibit a regulatory con- 

 nexion with one another, as is indeed the case in every metabolic process. 

 Thus the secretion of an enzyme may begin only at a certain stage of 

 development 2 , and may be influenced by the food supply or by other 

 external agencies. In Dionaea pepsin is excreted only after an insect has 

 been captured, i. e. only under the action of a chemical stimulus, and in many 



1 Beyerinck states that a green alga, Scenedesmus acutus, also liquefies gelatine (Bot. Zeitung, 

 1890, p. 729). 



2 For example in case of invertase, see Wasserzng, Ann. d. 1'Inst. Pasteur, iSSS, T. I, p. 525 ; 

 Bourquelot u. Graziani, Bot. Centralbl., 1893, Bd. LV, p. 326; in case of diastase, Duclaux, Ann. 

 d. 1'Inst. Pasteur, 1889, T. Ill, p. 107. 



