146 Autonomy of Cell-Organs 



which possess special chromatophores. Hence we must 

 imagine them to have originated from the others through 

 differentiation. A further step in the differentiation is 

 then the development of colorless conditions of these 

 chromatophores. These are still lacking in the lower Al- 

 gae, occur first in the highest groups of this class, and at- 

 tain their full significance only in the higher plants. In 

 other words, we must regard the amyloplasts, although 

 they are generally the young condition from which chlor- 

 ophyll bodies develop, as the consequences of a higher 

 differentiation and assume that they have developed phylo- 

 genetically from the latter. This discussion is important 

 for the reason that it brings nearer to our understanding 

 the not infrequent changes of form of the trophoplasts on 

 the germ-tracks. On the whole, the cells of the germ- 

 tracks of the higher plants are, as many authors empha- 

 size, of an embryonic nature, and such cells probably 

 always possess colorless trophoplasts. But according to 

 our definition of the germ-tracks, there are many excep- 

 tions to this rule. Thus, to name only one instance, the 

 prothallia of ferns, in their youthful state, consist of 

 green, dividing cells, with well-formed chlorophyll-grains, 

 from which later the amyloplasts of the egg-cells will 

 originate. Also in the callus-formation of cut petioles of 

 Begonia, Peperomia, and other species, a reversion of 

 green trophoplasts into colorless ones may take place, 

 especially in the case of the production of adventitious 

 buds. And, since generally the amyloplasts occur in young 

 cells and their derivates in grown protoplasts, these and 

 similar cases would be illustrative of a pronounced reju- 

 venation. 



' On the germ-tracks the amyloplasts usually take on a 

 simple roundish form, on the somatic tracks they change 



