TKANSAOTiONri Ul' SECTION K. 903 



With the information acquired, as to the effect of direct sun-rays upon plants, 

 trials were made in the direction of forcing plants to protect themselves against 

 those direct rajs which, in the clear South African atmosphere, at an altitude of 

 4,550 feet, were proved to he distressing to them. Nasturtiums were selected as 

 most likely to he sensitive to the treatment they were to be exposed to, and trials 

 were commenced with an existing group of growing common nasturtiums, which 

 were already in a suitable aspect, and were shaded by a brick wall at certain 

 hours of the day from all direct rays. Between April 21, 1905, and August 5. 

 1907, the whole of the group had been cbauged from the ordinary scarlet au<l 

 orange varieties into a new mauve variety, with the exception of one plant, whose 

 flowers were changed to the deepest carmine, with velvety-blue markings on two 

 of the petals. A seed from this plant, which was brought from Pretoria and 

 sown under glass at York on March 26, 1908, was changed to the mauve variety 

 by exactly similar treatment at York to that administered in other cases at 

 Pretoria in order to produce the mauve variety from the deep carmine. 



The principle which has heen followed is to shade off with a perfectly opaque 

 screen all direct rays of the sun for certain intervals of daylight. There has been 

 no other special treatment, and the only fertihsers used have been soot-water and 

 liquid manure. Their judicious use during the correct periods of growth, and 

 their supply in proper strengtli, are considered of great importance. 



At Pretoria the mauve variety proved a veritable mutation, and no known 

 instance occurred of its reverting to the original. Experiment so far goes to show 

 that seeds from it after the second year may he planted in any aspect, and will 

 come true even if sown in such different climates as those of York and Pretoria. 



The crimson variety similarly treated in York and in Pretoria gave the same 

 flowers of a bronze old-gold colour in both places, and the seed of this latter 

 variety brought from Pretoria and sown in York gave the same curious colour, in 

 spite of the great difference of altitude between the two localities. 



Cuttings of the mauve variety could he grown in any aspect at Pretoria, with- 

 out any change in the mauve colour of the flowers. 



In addition to the mauve and bronze old-gold colours, varieties of rose-salmon 

 and of sallow flesh-colour have heen obtained, and no difficulty has heen ex- 

 perienced in changing any of the known orange, yellow, or scarlet flowers into 

 these curious colours. 



Experiments with dahlias and cosmos indicate that their coloration can be as 

 easily changed as that of nasturtiums by employing similar means. 



5. lite Mechanical and Electrical Response of Plants. 

 By Professor J. C. Bosb, C.I.E., M.A., D.Sc. 



In order to make an accurate study of the effects of external stimulus on the 

 plant, it is necessary to have some means of immediately recording the responsive 

 changes that take place. In making records of motile responses many difliculties 

 are encountered, owing to friction and other causes. The author has overcome 

 these by devising two different types of instrument. Of these the first is the 

 oscillating recorder, in which a very light aluminium recording-lever traces 

 response-curves on a moving surface of smoked glass, which touches the recording- 

 point at intervals of one-fifth of a second. Friction of the recording-point is thus 

 practically eliminated, and as the record consists of successive dots, it also gives 

 the time-relations of the curve. The second method of record employed is that of 

 the optical lever, which enables the movements even of minute leaflets to be self- 

 recorded. A very high magnification may be obtained by its means, and the 

 immediate effects of a given stimulus clearly observed. 



Again, by the employment of the method of balance, any variation in the rate 

 of growth under external stiiQulus finds immediate record. 



The author has also shown that a definite electrical change, of responsive 

 character, occurs in all vegetable tissues on excitation. Thus all plants, and all 

 organs of all planlg, are shown to be sensitive. 



