R. H. ROBERTS 349 



temperatures. The florigen particles are recovered by filtering or decant- 

 ing, and evaporating the remaining solvent at a temperature below 60° C. 



The particles are highly insoluble in such solvents as water, alcohol, 

 acetone, xylol, benzol, ether, ethylacetate, petroleum ether, ethanola- 

 mine, polyethylene glycol, and dioxane. This may be an explanation 

 of why attempts by numerous workers to obtain florigen have been 

 unsuccessfijl. The particles are poorly soluble in Dispersol. Consequently, 

 repeated extractions of the leaves yield added amounts of particles. 



No particles have been obtained from extracts of nonflowering plants 

 such as those growing in a photoperiod unfavorable to flowering or 

 from those plants which are not known to flower, as for example, some 

 varieties of sweet potato. Particles of a like physical appearance have 

 been obtained from 23 species of dicotyledons including Cuscuta 

 (Dodder) and Monotropa (Indian Pipe), and from six monocotyledons. 

 All flowering plants chosen for extraction have yielded particles. Tests 

 are under way to determine if these will have interspecific effects on the 

 induction of blossoming. Preliminary experiments directed towards char- 

 acterization of the extracted particles are also under way. 



A solution of the florigen particles in Dispersol can be applied to 

 plants being used in tests of flower induction by wetting the foliage 

 with it. Plants for a preliminary test of induction should be selected 

 from those with a systemic flowering habit, at least until more is known 

 of the factors determining the induction of plants which flower only 

 terminally. (Plants of the latter type, as Klondyke Cosmos, do not 

 become induced to blossom by grafting.) A plant should not be expected 

 to respond beyond its genetical potentialities. 



The limited action of the extract in inducing blossoming of cocklebur 

 comparable to that from only one or two long dark periods may indicate 

 that the present material may be a precursor rather than the actual 

 florigen. 



For several months after September, 1948, the induction studies 

 were interrupted by the accidental introduction of a volatile ester of 

 2,4-dichlorophenoxyacetic acid into the greenhouses. In March, 1949, 

 16 plants of 19 treated with extract became partially induced, again 

 to about the same degree as plants given one or two long nights. In 

 all 131 plants have been partially induced with plant extract. 



Interest has shifted for the present from the induction of blossoming 

 to the nature of the extracts which have been obtained. By varying 



