34^ PLANT GROWTH SUBSTANCES 



plant to be treated produced about the same degree of blossoming as 

 occurs on plants after exposure to one or two long dark periods (short 

 days). Subsequent trials with crude extract were 8 to lo per cent success- 

 ful. In January, 1948, small, colorless, isotropic granular particles were 

 obtained from the extract. When these were dissolved in fresh solvent 

 and applied to vegetative plants of cocklebur in a long-day environment 

 in March, all of the 15 plants which were treated formed staminate 

 blossoms comparable in development with those on plants which had 

 been given one or two short photoperiods (Fig. i). The macroscopic 

 blossom buds appeared after five to eight weeks. This amount of time is 

 typical of the period usually needed to produce blossoming from the 

 stimulus of a single long dark period. Seven of the 15 plants bore 

 pistillate blossoms similar to those on plants which have received two 

 short photoperiods. 



The extract was effective at as high a dilution as one part to ten 

 thousand. The effect from the solution was also additive to photoperiod. 

 Four plants given one short photoperiod and also sprayed with the 

 solution made a greater blossom development than those with only one 

 short photoperiod. A total of 43 cocklebur plants have been induced 

 to flower by treating them with plant extract. 



Other effects from applying the plant extract were to reduce cambial 

 activity and to induce maturation of tissues comparable to that resulting 

 from photoperiod treatments which bring about a like degree of blossom- 

 ing. The extract also inhibits callus formation in wounded areas of stems. 

 It has not yet been determined if a substance of a like physiological 

 activity would have a similar effect upon some animal tumors. 



The following procedure is used to obtain florigen particles. Soak a 

 small sample of fresh or frozen leaves taken from plants in flower in the 

 least practicable amount of a highly refined, odorless insecticide base 

 such as Shell Dispersol, for an hour or longer. This solvent is a non- 

 aromatic oil fraction recovered from kerosene and having an IBP of 

 387° F. and an FBP of 485° F. Squeeze out the solvent, remove and 

 discard the aqueous phase if any is present, and filter. A yellowish 

 pigment which seems not to interfere with florigen extraction or activity 

 is present in the extract from most species. Deep freezing at 0° F. or 

 below is used to initiate separation of the particles. This progresses 

 slowly for several hours or even days. The particles in extracts from some 

 plants, for example, white sweet clover or sweet corn, dissolve at room 



