42 THE CELL-WALL. 



important part in the process, and it will be necessary later on to discuss its 

 significance in this connection. 



The chlorophyll-bodies, mentioned already more than once incidentally, are 

 green corpuscles, roundish, ellipsoidal, or lenticular in shape, and grouped in a 

 great variety of ways (figure 25a, i, k, I, m, p). They are produced generally 

 in great numbers by the protoplast in special sac-like excavations in its body 

 but nowhere except where they are necessary, that is, in those cells wherein 

 the transmutation of inorganic food-stufis into organic matter takes place. This 

 transformation, so important to the existence of the organic world, will be con- 

 sidered in detail later on. Chlorophyll-corpuscles are not, as regards their material 

 basis, essentially different from the substance of the protoplasm in which they 

 are formed, and in which they remain embedded for life, but their green colour 

 distinguishes them very clearly from their environment. This greenness is due 

 to a colouring matter stored in the protoplasmic substance of the corpuscle; and 

 our ideas of plant-life are so intimately associated with this remarkable pigment, 

 that a plant that is not green seems to us to be almost an anomaly. 



Besides the nucleus and the chlorophyll-bodies or corpuscles, protoplasts pro- 

 duce starch-grains, aleurone-grains, crystals of oxalate of lime, and drops of oil, all 

 of which will be dealt with presently in their proper place. They are evolved in 

 accordance with the requirements of the moment and with the position held in the 

 edifice of the plant by the cells concerned. Moreover, the walls of the cells them- 

 selves are the work of the protoplasts, and it is not a mere phrase, but a literal fact, 

 that the protoplasts build their abodes themselves, divide and adapt the interiors 

 according to their requirements, store up necessary supplies within them, and, most 

 important of all, provide the wherewithal needful for nutrition, for maintenance, 

 and for reproduction. 



CONSTRUCTION OF THE CELL- WALL AND ESTABLISHMENT OF CONNECTIONS 

 BETWEEN NEIGHBOUEING CELL-CAVITIES. 



Of all these performances, the construction of the cell- wall shows the greatest 

 variety from the nature of the case. For the envelope with which each individual 

 protoplast surrounds itself serves at once as a protection for the delicate protoplasm, 

 and as a firm support for structural additions; and, at the same time, it must not 

 impede the reciprocal action betw^een the protoplasts and the external world, or the 

 intercourse between those living in adjoining cavities. These cell-walls are accord- 

 ingly very wonderful structures, and we shall often have occasion to discuss them, 

 especially with reference to the significance of variations in their structure in 

 particular cases. At present it is sufficient to remark that the original envelope 

 which is secreted from the body of a protoplast and which appears at first as a 

 delicate skin, is made of a substance composed of carbon, hydrogen, and oxygen, 

 belonging to the class of carbohj^drates. 



The name of cell-membrane, usually applied to the original envelope formed by 



