ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 625 



BOTANY. 



GENERAL. 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 Includingr Cell-contents. 



Chlorophyll -formation.* — N. Monteverde and W. Liubimenko have 

 studied the formation of chlorophyll in plants, and find that two dis- 

 tinct chemical processes are involved ; the first process converts colourless 

 leucophyll into an intermediate substance known as chlorophyllogen, a 

 coloured substance ; the second process results in the formation of green 

 chlorophyll, by the aid of light or of certain chemical substances. Light 

 is the usual source of energy, but Conifers and a few other plants make 

 use of unknown chemical agents. Before forming chloryphyll, chloro- 

 phyllogen is converted into a pigment, which is slowly transformed into 

 chlorophyll ; this pigment may be found in Ijoth living plants and in 

 those that have been killed by drying, but chlorophyll itself can only be 

 formed in living plants ; moreover, etiolated plants gradually lose their 

 power of converting the pigment into chlorophyll. The maximum 

 accumulation of chlorophyll corresponds to the maximum intensity of 

 light, but the absolute value of the maximum accumulation varies with 

 species. Excess of light retards chlorophyll-formation, especially in 

 etiolated plants which are suddenly exposed to such excess ; this is 

 probably due to the destruction of the intermediate pigment. There is 

 a definite ratio between the chlorophyll and the yellow pigments which 

 accompany it, and are subject to the same factors for their formation, 

 but there is no chemical relation between them. The destruction of 

 chlorophyll is due to physiological causes. The preceding results appear 

 to indicate some important points concerning the chemical theory as to 

 chlorophyll-formation. 



Structure and Development. 



Vegretative. 



Pneumatodes of Begonia.f — V. Touk has studied the pneumatodes 

 of the stem of Begonia vitifolia, and finds that they are characterized by 

 the presence of epithelial tissue composed of a small-celled, thin-walled 

 epidermis with a cuticle which is almost imperceptible ; the stomata 

 have no air-pores, or only rudimentary ones which may be closed by 



* Bull. Acad. Imp. Sci. St. Petersburg, vi. (1912) pp. 609-30. 

 t Ber. Deutsch. Bot. GeselL, xxx. (1912) pp. 257-62 (1 pL). 



December 18th, 19V^ 2 u 



