ONTOGENY OF CHROMATOPHORES 



39 



the author's own observations, the growing-point of the stem of 

 Selaginella Kraussiana and S. Martensii contains minute spherical 

 leucoplasts, which become transformed into small pale-green chloro- 

 plasts at a distance of "15 to - 2 mm. from the apex (Fig. 5b). 

 In this case, each embryonic cell is provided with a single chroma- 

 tophore, which, to begin with, divides once for every division 

 of the cell ; at a later stage the chromatophores multiply more 

 rapidly than the cells. In the case of the pendent and Haccid 

 young leaves of many tropical trees, multiplication of the chromato- 

 phores is postponed until an unusually late stage of' development, 





Pig. 5. 



A. Egg-cell of Hyacinlhus nonscriptus, showing leucoplasts with included starch. 



B. Meristematic cells from the growing-point of the stem of Selaginella Kraussiana ; 

 each contains a single chloroplast, which lies closely appressed to the nucleus. 



C. Palisade-cell from a still colourless young leaf of Humboldtia laurifolia ; only a few 

 pale-green chloroplasts are present. A after Schimper. 



although the mesophyll may ultimately become very rich in chlorophyll. 

 Each palisade-cell of Humboldtia laurifolia or Maniltoa gemmipara, 

 for example, contains only one or two pale-green chloroplasts long 

 after the leaves have emerged from the embryonic state, at a time 

 when their internal differentiation is otherwise well advanced. This 

 circumstance accounts for the white or pale-pink hue which is 

 characteristic of young foliage of this type. 



Not only can the chromatophores of permanent tissues be traced 

 right back to the apical meristems, but the presence of these bodies in 

 the germ-cells can also be clearly demonstrated. This fact was 

 established first of all by Schmitz with reference to the asexual 

 resting-spores, zoospores and female gametes of Algae. The spores 

 of luyophyta and Pteridophyta likewise contain chromatophores, which 

 are particularly numerous and brightly coloured (green) in the 

 case of Eijuisi tn in. Schimper discovered pale-green chloroplasts in the 

 egg-cells of Anthoccros laevis and Atrichum undulatvm, and among other 

 Bryophyta ; the same observer was able to demonstrate the occurrence 



