346 THE LIFE OF THE PLANT 



are absorbed. This is graphically illustrated in fig. III. From 

 the line ab perpendiculars are drawn, the length of which corre- 

 sponds to the amount of carbonic acid decomposed in the 

 corresponding parts of the spectrum (I) in tubes i, 2, 3, 4, 5 (II). 

 The broken line i, 2, 3, 4, 5 (III) clearly shows the part of 

 the spectrum in the sphere of which carbonic acid is decom- 

 posed most energetically. 



Thus spectroscopic investigation serves to prove on the one 

 hand that certain rays of the sun, after having crossed 

 without any modification immeasurable depths of space, 

 on meeting on their way a chlorophyll granule cease to be 

 light any longer, disappear in performing work of some 

 sort. On the other hand, the experiment in the spectrum 

 just described points to the fact that it is these very rays 

 which cause the decomposition of carbonic acid into carbon 

 and oxygen, and are used up in this chemical work. We 

 may conclude that a complete correlation is to be observed 

 between the accumulation and expenditure of energy in the 

 plant. 



We have thus discovered the source of energy and also the 

 apparatus to which this energy is applied, i.e. the chloroplast. 

 We have seen the work done during the process ; we have now 

 to discover the product obtained, to follow the further fate of 

 the carbon liberated from the carbonic acid and to realise what 

 is produced from that carbon in the plant. Here our curiosity 

 can be satisfied by the microscope. 



We take a green organ of some kind, say a leaf, and dissect 

 it so as to investigate it under a microscope ; or, what is better 

 still, we take a vegetable body, such as a green alga, commonly 

 called green-slime, which can be directly observed under a 

 microscope. Having made sure that the chloroplasts do not 

 contain any foreign body to begin with, 1 we expose the 

 green organ to sunlight either in the open air or in an artificial 

 atmosphere containing carbonic acid, i.e. we place it under con- 

 ditions favourable to the decomposition of carbonic acid. 

 After some time we again investigate the chloroplasts under 

 a microscope, and discover in them colourless grains which were 

 not there before. It is easily proved that these grains consist 

 of starch. Among the properties of starch is that of turning 



1 Which is ensured by keeping the plant in the dark for some time. 



