394 SECTIONAL TRANSACTIONS.— J, K. 



15. Presidential Address by Dr. C. S. Myers, r.B.S., on The 

 Influence of the late 11". H. R. Rivers on ilie Development of 

 Psychology in (i recti Britain. (See p. 17'J.j 



15, Dr. C. \Y. KiMMiNS. — The Sense of Visual Humour in Children. 



McDougall's new theory of laughter — A comparison of the results obtained 

 by investigations of verbal and visual humour — What sights children laugh at 

 most at different ages — Results of analyses of children's records — The effect 

 of rapid physical growth on the sense of humour — The difference in the sense 

 of visual humour in boys and girls under varying conditions at the same age — 

 The important part played in visual humour by the feeling of superiority — The 

 theories of laughter of Bergson, Freud, Boris Sidis, .Sully, and McDougall. 



Tuesday, September 12. 



17i Joint Discussion with Section H on Mental Characters and 



Race. Opener: Prof. J. L. Mtres. 



18. Dr. F. C. Shrubs-^el. — What is Mental Deficiency? 



19. Dr. G. A. AuDEX. — Types of Mental Deficiency. 



SECTION K.— BOTANY. 



(For references to the publication elsewhere of communications entered in the 

 following list of transactions, see p. 410.) 



Thursday, September 7. 



1. Dr. W. H. Pearsall and Prof. J. H. Priestley.— Lea/ Growth. 



Leaf growth is considered from the point of view of form variations in given 

 types of leaves. Since the latter, in any species, appear to be largely due | 

 to external factors, a starting point is presented for the consideration of theJ 

 internal mechanism affecting leaf form. Two main internal factors are recog- 

 nised : (1) hydrostatic pressure, (2) the pei'meability of the cell walls in thej 

 meristematic tissues. | 



Leaf growth ceases, or is much restricted, by negative hydrostatic pressures, ! 

 and may be increased by positive pressures. Daily and seasonal variations in! 

 growth-rate agree with this fact, also the variations in the size and form of] 

 leaves produced under experimental conditions. 



Other modifications of leaf shape under diverse light conditions appear to be 

 due to alterations in permeability of the walls of the meristematic cells. 



The supply of nutrient solution to the growing points is affected not only 

 by these two factors, but is also a resultant of the position of the growing] 

 points in relation to vascular supply. 



2. Dr. I. Soar. — The Structure of the Endodermis in Some Gymno- 



sperm Leaves. 



The leaves of some Gymnosperms, and especially those of the Abietinese, 

 show a well-marked endodermis, the cell walls of which are usually thickened. 

 Where modification of the endodermal wall occurs, the radial walls are suberised 

 and pitted, whereas the transverse walls are unpitted. In both cases the 

 suberin is deposited as a surface layer on either side of a lignocellulose 

 The nature of the tangential walls varies ; they are frequently lignifiec 



core, 

 ified and 



