SECT. I 



MORPHOLOGY 



63 



FIG. 64. Cell from the 

 upper surface of the 

 calyx of Trapaeolum 

 majus, showing chromo- 

 ]. lasts, (x 040.) 



chlorophyll-green of their chloroplasts changes to a brownish green 

 pigment, but in the following spring regains its 

 characteristic colour. 



In such phanerogamic parasites or humus- 

 plants as are devoid of green colour, the chloro- 

 plasts either do not develop, or they are white, 

 or have only a brownish or reddish colour. No 

 chromatophores are found in the Fungi. 



Leueoplasts. In the interior of plants, 

 where light cannot penetrate, leucoplasts are de- 

 veloped from the rudiments of the chromato- 

 phores instead of chloroplasts. They are of a 

 denser consistency than the chloroplasts, mostly 

 spherical in shape, but often somewhat elongated 

 in consequence of enclosed albuminous crystals. 

 If the leucoplasts become at any time exposed to 

 the light, they may change into chloroplasts. 

 This frequently occurs, for example, in the super- 

 ficial portions of potato tubers. 



Chromoplasts. The chromoplasts of most 

 flowers and fruits arise either directly from the rudiments of 

 colourless chromatophores, or from previously formed chloroplasts. 

 In shape the chromoplasts resemble the chloroplasts, except that 

 they are usually smaller ; in consequence of the crystallisation 

 of their colouring pigment they sometimes 

 assume a triangular, tabular, needle, or fan- 

 shaped form (Figs. 64, 65). The colour of the 

 chromoplasts varies from yellow to red, accord- 

 ing to the predominance of yellow xanthophyll 

 or orange -red carotin. The name carotin has 

 been derived from the Carrot (Daucus Carota), 

 in the roots of which it is particularly abundant 

 (Fig. 65). The frequent crystalline form of the 

 chromoplasts is, in a great part, due to the 

 tendency of carotin to crystallisation, although 

 it may be also occasioned by needle-like crystals 

 of albumin. Xanthophyll, however, is never 

 ,, f present in the chromoplasts except in an amor- 

 phous condition. 



Carotin is practically identical with the 

 chrysophyll found in the chloroplasts. Its 

 spectrum only differs from that of chrysophyll in having the absorp- 

 tion bands slightly displaced towards the violet end ( 46 ). 



Origin and Structure of the Cell Wall ( 47 ). The membrane which 

 encloses the vegetable protoplast is a product of the protoplasm. 

 Many low organisms belonging to the Algae liberate naked protoplasts 



KIG. Go. Cliromoplasts 

 the Carrot, some with 

 included starch grains. 

 (X 540.) 



