CHAPTER XVIII 

 THE FORMATION OF FLOWERS IN BRYOPHYLLUM 



The plants growing in the open in Bermuda differ in two 

 respects from the plants raised in my greenhouse in New York. 

 The Bermuda plants growing in the open have flowers in Febru- 

 ary or March, and furthermore they form a considerable 

 amount of a purplish pigment (anthocyanin?). Only in shaded 

 places did I find plants in Bermuda which had no flowers and 

 little or no purplish pigment. They were plants which, if my 

 memory does not deceive me, were only exceptionally or not at 

 all reached by direct sunlight. 



The plants in my greenhouse have, with a few exceptions, pro- 

 duced no flowers and little purplish pigment. The few plants 

 which produced flowers were in that part of the greenhouse 

 which had the strongest light. It is not impossible that those few 

 plants which produced flowers had been illuminated for short 

 periods by direct sunlight which reached them through the open 

 transom, without the rays of light having been filtered through 

 the glass plates of the roof of the aquarium. It is, however, 

 quite probable that the failure of my plants to produce flowers 

 was connected with the comparative lack of light, and possibly 

 with the lack of ultraviolet light. 



Sachs pubhshed a paper in 1886^ in which he tried to prove that 

 ultraviolet light is necessary to produce flowers. He had shown 

 in previous papers that the production of flowers can occur in 

 the apex of Tropaeolum majus even if this apex is kept in the dark, 

 provided the leaves of the plant are exposed to sufficiently strong 

 light. This observation formed the basis of his hypothesis of 

 specific or organ-forming substances which are transported in the 

 sap sent out by the leaf. 



' Sachs, J.: ArheUen d. hot. Inst, in Wiirzburg, vol. iii, 372, Leipzig, 1888. 



140 



