40 HUTCHINSON'S POPULAR BOTANY 



A"lge, which multiply to such an extent in their substance that the entire 

 animal is coloured green. After its larval stage the worm does not need 

 to trouble about food, for the plants manufacture and supply it with starchy 

 products. The plants in turn needing nitrogen, which is a rare commodity 

 in the sea, obtain it from the animal's waste. This partnership is not an 

 occasional or chance affair : both plant and animal have so thoroughly 

 entered into it through many generations that it has become fixed and 

 habitual, like the association of Algse and Fungus which has resulted in the 

 production of thousands of species of the compound plants we know as 

 Lichens. Professor Keeble has devoted a small volume entirely to telling 

 the story of the relations between these very dissimilar organisms.* 



Under the microscope the chloroplasts have usually a globular appear- 

 ance, but instances occur in which they- are quite formless. In the 

 well-known Water-thyme (Elodea canadensis), so execrated by bargemen 



and water-mill owners, they are 

 irregular in shape, some presenting 

 the appearance of circular flattened 

 discs, while others are spherical and 

 oval. Their diameters vary from 

 ^oVoth to ^nroTjth f an inch. Of 

 the colouring matter diffused 

 through the corpuscles, we have as- 

 yet no certain knowledge, but th^ 

 opinion still held by very many 

 that it is composed of two inde- 

 pendent colouring substances a 

 golden-yellow and a blue-green is 



FIG. 63.-STAKCH-GBAINS OF POTATO. now abandoned by the highest 



authorities. Those substances are, 



indeed, the products of the decomposition of chlorophyll, but chlorophyll 

 itself is a single pigment. 



One eminent analyst (Gautier) regards it as related to the colouring 

 matter of the bile : another (Hoppe-Seyler) as a fatty body allied to lecithin, 

 which is a phosphoretted viscous substance entering into the formation of 

 the brain. But " it is extremely difficult," says Dr. Reynolds Green. " to 

 say what is the chemical composition of chlorophyll, on account of the 

 readiness with which it is decomposed. In all the processes which have 

 been adopted for its extraction it undergoes decomposition, and consequently 

 no definite conclusions as to its chemical nature can at present be arrived 

 at. It can be made to yield definite crystals by appropriate methods of 

 treatment after extraction, but it is probable that these crystals are a 

 derivative of chlorophyll, and not the pure pigment." The statement found 

 in many of the text-books that the chloroplasts are coloured blue by iodine 

 * Keeble, Plant-Animals : a Study in Symbiosis, 1910. 



