THE FOOD OF PLANTS. 31 



10. The Formation of Chlorophyll. 



A few seeds of Lupinus are germinated in darkness, e.g., in a 

 cupboard, in garden soil * contained in flower-pots. It is by no 

 means perfectly easy to make a place in which almost absolute 

 darkness prevails, and if we wish to cultivate plants in absence 

 of light, this must not be lost sight of. It is however sufficient 

 for our purpose here to place the flower-pots in the cupboard, under 

 an opaque cardboard receiver, and carefully plug the keyhole of 

 the cupboard. 



The hypocotyl and the cotyledons soon appear above ground, if 

 the conditions of germination are moderately favourable. The 

 cotyledons however are not green like those of Lupin seedlings 

 grown in the light, they are yellow in colour. If we examine 

 transverse sections of the cotyledons under the microscope, we 

 see clearly the epidermis, the vascular bundles, and the leaf 

 parenchyma. The cells of the last, especially the more peripheral 

 ones, contain, besides other constituents, small yellow granules, the 

 etiolin grains. If the seedlings raised in the dark are exposed to 

 the light, they soon become green, and we now find chlorophyll 

 grains in the cells of the leaf parenchyma. These are developed, 

 under the influence of the light, from the etiolin grains, from 

 which they differ not only in their green colour but also in their 

 greater size. If seedlings of Phaseolus or Pisum are developed 

 in darkness, they produce long white stems and small yellow 

 leaves. I found that the leaves of pea seedlings, brought into the 

 light after forming several internodes in darkness, did not all 

 become green. The younger leaves certainly formed chlorophyll. 

 The oldest ones, however, remained yellow. 



Most plants form normal green chlorophyll only in access of 

 light; some however become green even in the dark. If, e.g., 

 seeds of Pinus sylvestris are sown in garden soil, and germinated 

 in absence of light (germination proceeds comparatively slowly), 

 ,the root first breaks forth. Then the hypocotyl extends, at first 

 however appearing with a knee bend, since the cotyledons still 

 remain in the seed. Finally the cotyledons emerge from the 



* It may here once for all be remarked that for culture experiments it is 

 generally best to employ the dark, very humous soil used for greenhouse plants. 

 The soil is just so much moistened that it can still be broken down between 

 the hands into a finely crumbled mass, which is then thrown on to a sieve with 

 meshes 1-5 mm. square, and riddled into the culture vessels. 



