64 PROCEEDINGS OF TTIR 



riaiit-sporls produced :it will. 

 By Col. II. E. Rawso.v, CM., K.E., F.L.S. 



I Head r.tli N(iM-mlnT, VJV.".] 



The observation that slinibs of lvei-a|)i)lo (Aherla caffra) near 

 Capo Town died when tliey were deprived of full sun up to a 

 certain altitude in the early morning, led to experiments in screen- 

 injj; ve«,'utables at this hour for various periods. The results 

 obtained sui^gested a system of screening plants at selected 

 intervals of daylight, to which the term "selective screening" 

 was ap|)lied. A new variety of TroimoJam raajas appeared in 

 consequence, and re-ap])eared amongst the seedlings in following 

 years which were similarly screened, eventually becoming fixed. 



AVell-kuown sports began to a])pear in 'J'ropavluiu ])laMts, such 

 as an increased number of spurs, proliferation, and leaf-division, 

 which also reappeared when the same selective screening was 

 adhered to. 



These sports and several new varieties of 2\ majus, as well as 

 many correlated variations, re-appeared in the open garden w ithout 

 selected screening. 



The experiments were extended, and a new single form of 

 Papaver li/ueas which was desired was obtained. From this 

 single Poppy a double form aj)peared which has become fixed. 



iSterilitv was very marked in all cases of sudden changes of 

 colour or structure, indicating that the reproductive oi'gans were 

 atfected by selective screening. Proliferation and the transoiission 

 through the seed of the changes in colour and structure also point 

 to the organs being influenced during, as well as subsequent to, 

 the action upon the soma ; while leaf-division., increased spurs, 

 and the correlated variations therewith, prove that the soma of 

 the plant has been affected generally by the sci'eening. The 

 intensity of the light regidates and modifies the coloured bands 

 upon all parts of a plant which have been excited by interference. 



hi nature, selective screening prevails very universally, and these 

 experimtujts suggest that it deserves to be studied for its power to 

 brinf out potentialities which are known to be latent, and to 

 cause correlated variations. Insect-visitors give rise to coloured 

 bands. 



Kecent American research (5) gives support to the views set out 

 in this abstract. 



Jieferences to Literature. 



1. 1J\AVS0\, Col. II. E. — Snnrise and Growth. Iiep. S. Afr. Assoc. 



n»0o (11.1U7). pp. L>r,i-i>r)0. 



2. Colour Cliangvs in Flowers pvodiicod bv coiitrolliii(>: Insolation. 



Uep. Brit. Assoc, Dublin, 11)08 (li)09), pp. 9(J2 903. 



3. Variation of Striictuve and Colour of Fhnvers under Insolation. 



Ihid. r>innint;bani, 191;'. (1914), pp. 711-713. 



4. Chanjii's of Colour and Structure of Flowers by removing 



Sunli<rlit at selected hours. London ; Jouru. K. llovt. !Soc. 

 xli. (1915), pp. 4i.'-4t). 



