SEASONAL ACTIVITIES OF PLANTS. 231 



equable temperature during the entire year. But this stimulus 

 is not to be thoug'ht of as always a change from a low to a high 

 temperature, for the reverse may have a like effect. Encelia 

 farinosa is a desert shrub which has been introduced into the 

 austral plantation of the Desert Laboratory at 6,000 feet, being 

 taken from a habitat at 2,500 feet and correspondingly warmer. 

 It is a winter perennial, however, and its season of activity lies 

 within the cool season of February to April, at which time it goes 

 into a resting condition. ISTow, if the roots are taken up at this 

 time and carried up to the 6000-foot level, the stimulus of 

 change to the cooler temperature again causes it to awaken and 

 put out a new set of shoots. Exact obseiwations upon this stim- 

 ulative reaction of any plant are possible, and many of the prac- 

 tices of the gardener are the results of long practical experience 

 upon the matter. An interesting set of data have recently been 

 obtained by Dr. B. E. Livingston with respect to the change from 

 the infra-optinnnn to the optimum with regard to moisture from 

 which it is seen that seeds of Cereus, Fouqueria, Phaseolus and 

 Triticum, germinated when transferred from an air-dry condi- 

 tion to soil containing 15 per cent, of water, Impatiens in soil 

 containing 20-25 per cent. Raplianus demanded 20 per cent., and 

 Trifolium 25 per cent. 



Gradual changes in the temperature, or in any of the other 

 agencies affecting plants, may allow the protoplasm to make such 

 adjustments of the living matter that the cardinal points arc 

 much changed and a species may accommodate itself to condi- 

 tions ordinarily unendurable. Experimentation in this phase 

 of the subject has been carried on most with bacteria and the 

 simpler fungi, and it has been found that these organ'sms arj 

 capable of making such slow changes as to be able to undergo 

 temperatures, comparatively very low and very high. The facil- 

 ity with which these organisms may be handled has also led to 

 the result that they have been found to accommodate themselves 

 to very great changes in the composition of the nutrient medium, 

 and to endure the presence of poisonous substances, the concen- 

 tration of which was increased very gradually. 



