58 IV. PLASTIDS. 



however, is what in this case determines the form, only a small 

 quantity of- protoplasm adhering to it, from which the starch 

 grains arise. 



Coloured Leaves. If we examine also one of the coloured 

 varieties of our shrubs or trees, such as the copper-beech, or else 

 an herbaceous plant with leaves coloured reddish-brown, such as 

 the beetroot, we see that the cells of the epidermis contain a 

 rosy cell-sap, and that therefore the joint action of the red of 

 the surface and the green of the interior gives the reddish-brown 

 compound colour. 



Autumnal Colours. In the autumnal coloration of the leaves 

 of the Virginian creeper, Ampelopsis hederacea, we can determine 

 that the rose-coloured cell-sap arises in the cells of the internal 

 tissue, and not of the epidermis. The yellow autumn tints of 

 leaves depend on the yellow colour of the disorganised chloro- 

 phyll bodies, as is shown in the most beautiful way in the leaves 

 of. the Maidenhair tree, Ginkgo biloba (Salisburia adiantifolia),. 

 or, failing this, those of the various species of Maple. Brown 

 autumn tints of leaves may arise from a corresponding staining 

 of the cell- walls, but chiefly, however, from the cell-contents, as 

 is easy to determine in the case of the Oak. 



Origin of Starch. Starch grains are found in certain special- 

 ised protoplasmic structures. We have already recognised chloro- 

 phyll bodies in this capacity, also certain other colour-bodies in 

 which starch grains are often present ; and have also made 

 reference to colourless starch formers. Upon these last devolves 

 the formation of starch in the deeper layers of the body of the 

 plant. We can comprise all three structures under the name 

 of Chromatophores, and distinguish chlorophyll bodies, colour- 

 bodies, and colourless starch-formers as Chloroplasts, Chromo- 

 plasts, and Leucoplasts respectively. These structures have 

 similar origins, and can be transformed into one another. They are 

 living constituents of the protoplasm of the cell, and lie embedded 

 in the cytoplasm. On the other hand the blue stars, which we 

 found in the cell-sap of Delphinium consolida, only represent 

 colour-material crystallised out from the cell-sap, and are, like 

 the lumps of colour-material which we found in the red cell-sap 

 of Verbascum nigrum, not to be reckoned as chromatophores,. 

 which latter, are essentially protoplasmic bodies impregnated with 

 colour -'material. 



Leucoplasts of Phajus. The largest and most beautiful starch 



