MECHANISMS FOR CONVEYANCE TO AND FRO. 465 



form a constituent of the protoplasm of the fermentative organism, and themselves 

 affect and decompose their environment through the cell-wall. 



The most important enzymes are, first, pepsin, which peptonizes albumens 

 in the presence of weak acids, i.e. changing them into a soluble condition, whereby 

 they are enabled to pass througli the partition-walls fi'om one cell-chamber to 

 another. The pepsin contained in plants does not, indeed, differ from that in the 

 gastric juice of animals, so that the part performed in both cases is essentially 

 the same. In the stomach of animals it has to perform the important task of 

 bringing the albumens taken in as food into a soluble form, so that they can 

 then enter the blood. The presence of pepsin in insectivorous plants has already 

 been alluded to. Another enzyme to be mentioned is diastase, which makes 

 starch grains soluble, since it decomposes them into sugar and dextrin. It is 

 found wherever stai'ch-grains have been stored up when they are again to be 

 utilized and to be assimilated. Emulsin and myrosin should also be pointed 

 out. They decompose glucosides in the manner already described, and thereby 

 give rise to sweet sugar, especially in fruits; but they can also effect various 

 other decompositions, as, for example, the splitting up of the amygdalin contained 

 in almonds into glucose, prussic acid, and oil of bitter almonds, which is effected by 

 emulsin. Papain, occurring in the fruits of Garica Papaya, and invertin, which 

 has been observed in Yeast, are to be regarded as enzymes. All substances which 

 have a decomposing action on their environment, without at the same time under- 

 going any chemical change themselves, are called ferments, and, so far, all enzymes 

 are to be considered ferments. It has been demonstrated, however, that under 

 certain conditions, acids — for example, phosjjhoric acid — and even water at a high 

 temperature, exhibit a ferment action, and for this reason the name enzyme has 

 been chosen for the nitrogenous compounds detailed. 



We have now enumerated the most important of those substances whose 

 building up and breaking down, whose transformations and interactions constitute 

 wliat we recognize as the life of plants. 



2. TRANSPORT OF SUBSTANCES IN LIVING PLANTS. 



Meclianisms for Conveyance to and fro. — Significance of Anthocyanin in the Ti'ansportations and 

 Tran-sformations of Materials. — Autumn Colouring of Foliage. 



MECHANISMS FOR CONVEYANCE TO AND FRO. 



It has already been explained that the decomposition of carbonic acid, and 



the formation of organic matter out of the absorbed gaseous and liquid inorganic 



food, can only occur in cells which contain chlorophyll-bodies. The shape and 



arrangement of the chlorophyll-corpuscles in individual cells, and further, the 



form and arrangement of these green cells themselves, have also been there 

 Vol. I. 30 



