CRITICAL FLOWERING AND FRUITING TEMPER- 

 ATURES FOR PHYTOLACCA DECANDRA 



FRANCIS E. LLOYD 



McGill University, Montreal, Canada 



The behaviors of the poke-weed {Phytolacca decandra) in two 

 diverse climates, widely different from its own, those namely of 

 Tucson, Arizona, and Carmel, California, have been observed 

 for several years by Dr. D. T. MacDougal and the writer. Of 

 these behaviors perhaps the most interesting is the failure to 

 reproduce by seed at Carmel, in contrast with Tucson where 

 fruits and seeds are formed in abundance. At first blush it 

 would seem that this contrast is due to temperature relations, 

 and this turns out to be the case. Indeed, as it has happened, 

 the temperature relations are so clearly indicated in the be- 

 havior of the plant at Carmel, that it is possible to determine, 

 within a very small error, the critical flowering and fruiting 

 temperatures. Since the plant grows well enough though not 

 quite normally! in this locality, attaining a stature of a meter 

 more or less, and making a consistent, but under the circum- 

 stances unsuccessful attempt at flowering, it appears that the 

 failure in this constitutes the factor limiting its ability to per- 

 sist unaided. Under exceptional circumstances, however, seed 

 may be produced, and it is these circumstances which afford 

 the data herein offered. 



Before presenting data, the cogency of which rests upon an 

 understanding of the climate during the growing season at Car- 

 mel, a brief summary of this will be given. In the accompany- 

 ing table, the temperature ranges for ten weeks are spread, to- 

 gether with the numbers of days having temperature ranges 

 included within limits of five degrees as indicated. On days 

 having temperatures not higher than 70° there is usually no 



1 Ann. Rep. Dept. Bot. Res. Carnegie Inst. Wash, for 1914, p. 71. 



121 



