I30 THE PHYSIOLOGY OF PLANTS 



and will give expression to all the characters which we recog- 

 nise in the adult plant. 



Though we have stated that the various groups of sub- 

 stances of the protoplasm cannot as yet be microscopically 

 differentiated, we must modify the statement to exclude a few 

 cases. For we can recognise in every young cell of a leaf, 

 and of other tissues too, a number of small indistinct par- 

 ticles of a very dense protoplasmic nature, which are termed 

 trophoplasts,'*' which have in many cases very important functions 

 to perform. A number of these bodies, for instance, develop the 

 green colouring matter, and become ehlorophyll eorpuseles, i.e., 

 the chief formative bodies of the cell ; others become brightly 

 coloured, and form the ehromoplastids which are found in 

 flowers and fruits ; and, finally, a third group, which remains 

 colourless, leucoplastids, can form starch grains out of sugars. 



All these trophoplasts grow within the cell and increase in 

 number by division. A number of them are carried into the 

 daughter-cells during division, and we can therefore rightly 

 say that the chlorophyll granule, for instance, in the uppermost 

 cell of a Rioinus plant several yards in height, is derived from 

 one of the chlorophyll bodies of the embryo. 



When the trophoplast becomes transformed into a chloro- 

 phyll corpuscle, it becomes more porous and sponge-like, and 

 in its interstices the actual colouring fluid makes its appear- 

 ance. The latter consists of two substances — namely, the 

 green chlorophyll and the yellow xanthophyll. The nitrogen- 

 containing chlorophyll (recently shown to be devoid of iron) 

 can be extracted from the cells by alcohol, ether, chloroform, 

 or by etherial and fatty oils. It then has the appearance 

 of a green solution with a blood-red fluorescence. It is a 

 very unstable substance even within the vegetable cell, and 

 as soon as the latter dies the acid cell-sap gives it a brownish 

 colour. By this action acid chlorophyll or hypoeMorin (chloro- 

 phyllan, phyllo-cyanic acid) is formed, and this is the cause of 

 the spotting of diseased leaves. If in the cooking of green 

 vegetables we wish to avoid such a discolouration, we need 

 only add a little carbonate of soda, as the presence of alkalies 

 will prevent the formation of the hypochlorin. 



' They are also called plastids, chfomatophores, leuHtes. 



