APPENDIX 507 



modating themselves to water as regards their vegetative activity, remain 

 with few exceptions subaerial plants as regards sexual reproduction. 



A more recent contribution to this subject is to be found in a 

 paper by Professor Klebs on the influence of environment on the 

 forms of plants in Darwin and Modern Science (1910). The circum- 

 stances favourable to growth, he remarks, difter from those which 

 promote reproduction. As he shows, the behaviour of a plant can be 

 determined at will by increasing or decreasing the supply of water and 

 mineral salts. In the first case, as in the ordinary treatment with 

 manure and abundant water, there is a relative diminution in the 

 production of organic substances, such as starch, sugars, etc., which 

 favours vegetative growth at the expense of the flowering process. If, 

 however, the supply of water and salts is diminished, as when the plant 

 grows under ordinary poor conditions, a vigorous production of organic 

 substances follows and flowering results. 



In this connection I may refer to the behaviour of the Sweet 

 Potato (Convolvulus Batatas}^ which rarely seeds except when grown in 

 poor, sandy soil, and in dry, rocky situations. The Fijians, I found, 

 were quite incredulous as to its maturing seed ; but after much 

 searching I found a solitary plant in seed and so relieved their doubts. 

 Similarly, the coloured people of the Turks Islands in the West 

 Indies were surprised when I showed them the seed from their own 

 plants. In the arid, sandy soil of those islands I found the plant 

 seeding freely. 



NOTE 31 (see previous note). 

 Growing Stakes or Live-Fences in Jamaica. 



NUMEROUS trees supply the Jamaicans with materials for living 

 posts for the wire-fences. These posts are employed to take the place 

 of the dead-wood posts of logwood. Limbs of such trees cut to a 

 length of from 4 to 6 feet are placed in the ground, and in a few 

 weeks they strike root and produce young leaves. 



Several of them belong to the Terebinthaceae, such as the Hog-plum 

 (Spondias lutea\ the Sweet-plum (Spondias purpurea\ the Maiden-plum 

 (Comocladia integriplia\ and the Birch (Bursera gummifera}. Amongst 

 other trees thus utilised may be mentioned the Cedar (Cedrela odorata\ 

 one of the Meliaceae, the Calabash- tree (Crescentia Cujete\ of the Cucur- 

 bitaceae, the Cocoa-plum (Chrysobalanus lcaco\ of the Chrysobalaneae, 

 and the Physic-nut (Jatropha Curcas\ of the Euphorbiaceae. Amongst 

 the Leguminosae thus employed are the Sword-plant, a species of 

 Erythrina (perhaps E. corallodendron\ and the Cuba-plum, which may 



