The Somatic Tracks 101 



celled somatic tracks which do not ramify any further, as 

 for example, the wood-fibres of some trees which are pro- 

 duced by the cambium. 



The somatic tracks are, in general, the cell-pedigrees 

 of the single cells of the grown individual, with the excep- 

 tion of the germ-cells. In the case of every cell and every 

 cell-complex one can trace them back to the germ-track 

 from which they have evolved. In plants all the profusely 

 branching primary and secondary germ-tracks are prob- 

 ably closely set, along their entire length, with such bushy 

 lateral twigs. These give its characteristic appearance to 

 our picture. In the Diptera they originate chiefly from 

 one point of the germ-track, and thereby the picture is 

 entirely changed. In the higher animals, however, they 

 gradually branch off from the unramified part of the 

 germ-track, and very greatly surpass it in the richness of 

 their further ramifications. 



The cells of the somatic tracks are usually composed 

 of the same protoplasmic organs as those of the germ- 

 tracks. Only here these organs are frequently adapted 

 to other functions, and therefore they bear other names. 

 Thus, in some somatic elements, the amyloplasts of the 

 germ-track cells become chloro'phyll-grains. Usually this 

 change is not only a more special adaptation, but also a 

 further differentiation. Especially do we meet again, al- 

 most without exception, in all somatic cells, such indi- 

 vidual parts of the germ-track cells as nucleus, tropho- 

 plast, vacuoles, nucleo-plasm, and lining layer. 



Against this general rule some individual exceptions 

 must be mentioned. I do not take into account the nu- 

 merous cells, such as the many wood-fibres, and the stone- 

 cells and cork-cells, which die soon after their development 

 and lose their entire protoplast. They render their ser- 



