402 SECTIONAL TRANSACTIONS.— K. 



Wednesday, September 13. 



22. Dr. W. E. G. Atkins. — Some Physical and Chemical Factors 



irliich affect Plant Distribution. 



In addition to temperature, moisture content, and intensity of illumination, 

 the salt and hydrogen-ion concentrations of the siti\ation appear to be im- 

 portant in determining distribution. This becomes clear when observations are 

 made on the soil supporting the same species in different localities. The soil 

 reaction may have a direct influence on the protoplasm of the roots, or it may 

 act indirectly by altering the flocculation, and consequently the aeration, of the 

 soil. It also affects the solubility of phosphates, iron salts, &c., causing 

 certain plants to become chlorotic so that they are crowded out under natural 

 conditions. Titrations of chloride, measurements of density, electrical con- 

 ductivity, freezing-point, and possibly of the critical solution-point with 

 phenol, of natural waters and soil extracts, may serve to map out the salinity 

 of various plant habitats. 



23. Prof. J. H. Peiestley and Dr. J. Ewixg. — Etiolation. 

 Plants show different types of growth reaction when grown continuously 



in darkness. Attention is here restricted to the reaction exemplified by Vicia 

 Faba, L., Pisum sativum, L., &c. The structural modifications produced in 

 these plants are consistent with the assumption that the meristem membranes, 

 when the stem is growing in darkness, remain relatively impermeable to the 

 supply of nutrient sap diffusing from the vascular bundles. The relative 

 impermeability of these membranes is also shown to be in accordance with 

 experimental and micro-chemical data. 



The presence of a functional primary endodermis in the stems of these 

 etiolated plants in regions where it is missing from the normal stem grown j 

 in the light is recorded, and the significance of this emphasised in relation to U 

 other structural features characteristic of etiolation. 



In the upper region of these etiolated stems the primary endodermis is re- 

 placed by a starch sheath, and at the same time the rounded outline of the stem 

 in cross-section changes, and it becomes angular, as in the stem grown in the 

 light. 



24. Miss Margery Knight. — Nuclear Changes in Relation to 



Different Methods of Reproduclion in the Eclocarpacece. 

 The Erfocarpacea show great variation in the origin and development of 

 motile reproductive cells. At different times and under different conditions one 

 individual plant produces sexual, asexual, and neutral swarm-spores. These 

 bodies show great variety in constitution, size, and behaviour. An inquiry into 

 the nuclear structures accompanying these variations shows that in the life- 

 cycle there is no rigidity of nuclear mechanism. The results of investigation 

 demonstrate the extent to which cytological changes may be influenced by 

 certain environmental factors. 



25. Prof. J. C. Schoute. — The Foliar Origin of the Internal Stelar 



Structure of the Marattiacea . 



26. Miss Violet M. Grubb. — Notes on the Reproduction of certain 



members of the Rhodophycea. 



{a) Porphyra vulgaris, Ag. 



Material gathered so far offers no decisive evidence of the presence of 

 asexual spores in this species, as stated by Berthold, but the disputed fact of 

 sexual reproduction is confirmed. 



An attempt has been made to determine the fate of the carpospores by 

 germinating them in cultures in order to verify the recent statement by Yendo 

 on the production of micro- and macro-gametes. 



(6) Hhodymenia palmata, Grev. 



The only form of reproduction hitherto known has been by tetraspores, and 

 as recently as 1919 Church quoted this species as one in which the sexual 

 phase bad been omitted from the life-cycle. 



