

BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 Including Cell-Contents. 



Origin of Chromoplasts and Pigment-formation.* — A. Guillier- 

 mond publishes the results of his investigations concerning the origin of 

 chromoplasts and the formation of pigments belonging to the xantho- 

 phyll and carotin groups. The pigments appear to be formed in three 

 different ways : — 1. A diffuse or finely-granular pigment is formed 

 within the mitochondrias or the chromoplasts arising from the mito- 

 chondrias. 2. The pigment formed within the mitochondrias or chromo- 

 plasts is at first diffuse or granular, but afterwards becomes crystalline. 

 3. The chloroplasts formed from the mitochondrias enlarge considerably, 

 and give rise to diffuse, granular, or crystalline pigments. The third 

 method is characteristic of the mesocarp and mesophyll of the majority 

 of fruits and flowers. This mitochondrial origin explains the elongated 

 form of all the simplest chromoplasts, which are, in fact, chondriocontes. 

 Finally, it is of interest to note that pigment-formation in plants is 

 effected by a process similar to that which has recently been observed in 

 animals. 



Structure and Development. 

 Vegetative. 



Epidermal Cells of Roots. f — Edith A. Roberts gives a summary of 

 work by previous observers on the factors governing the development of 

 root-hairs, and also the results of her own investigations. The plants 

 studied included barley, maize, lettuce, sunflower, and several species of 

 Cruciferge. The writer finds that the initial formation of the root-hair 

 is indicated by a general swelling of the outer wall of the epidermal cell. 

 The swelling is produced if the physical resistance of the wall is 

 overbalanced by the higher osmotic pressure which is maintained on the 

 inside of the wall ; further swelling followed by growth takes place at 

 the less resistant portion of the wall. This region bears no relation to 

 the position of the nucleus. The wall of the root-hair is composed of 

 two parts, an inner membrane of cellulose and an outer membrane of 



* Comptes Rendus, clxiv. (1917) pp. 232-5. 

 t Bot. Gaz., Ixii. (1916) pp. 488-506 (17 figs.). 



