188 



SCIENCE 



[N. S. Vol. LII. No. 1339 



1915 and in 1917, I brought forward addi- 

 tional facts bearing on the relation of the 0°, 

 10°, 15°, 20°, and 25° C. isotheres and added 

 arguments for the careful consideration of 

 the relation also of the 0°, 10°, 15°, 20°, and 

 25° C isocrymes, or lines of mean minima, 

 i. e., the mean temi)erature of the coldest 

 month, of the surface waters of the oceans, to 

 the demarcation, or division, points in the 

 marine floras. 



The various writers I have just cited take 

 up the subject of the relation of temperature 

 to distribution almost entirely from the dis- 

 tributional side. They show certain, at least, 

 of the relations of the intensity- and duration- 

 variables in their influence on those activities 

 of the organisms which make for persistence 

 in the particular localities where they are to be 

 foimd permanently. The activities controlled 

 are, imdoubtedly, all the necessarily vital 

 activities of the organism, but we may feel 

 fairly certain that those subject to the special 

 control of the limited temi>erature interval 

 are those more or less immediately con- 

 nected with reproduction. In general, it may 

 be said with some confidence, that the repro- 

 ductive activties are carried on at the maxima 

 of the temperatures at which the plant is 

 actively and most normally performing any 

 of its strictly vital functions. The initial 

 temperatures, e. g., those of the germination 

 of the seeds or spores, are undoubtedly lower, 

 in most cases at least, as are also those of 

 most rapid growth and those of the most 

 active metabolism. All, however, have their 

 optima which are the temperatures connected 

 with successful and orderly development, 

 within comparatively narrow limits and are 

 to be considered apart from the temperatures 

 possibly to be endured in states of rigor, but 

 without immediate death. Most of the physio- 

 logical experiments on the influence of tem- 

 perature on plants emphasize their sensitive- 

 ness as regards intensity, but do not yield 

 many data bearing on duration effects of 

 slightly unfavorable temperatures such as are 

 most desirable for assisting in the solution of 

 the problems of geographical distribution. A 

 notable and illmninating discussion between 



the two different points of view is shown in 

 the controversy between A. J. Ewart (1896 

 and 1898) and "W. and G. S. West (1898). 

 Ewart argues from the point of view of an 

 experimental worker in the laboratory, test- 

 ing under controlled conditions, while the 

 Wests bring forward from their long experi- 

 ence in the field, seemingly discordant facts. 

 Fhenologists are acquainted with many 

 facts that tend to show the close relations 

 existing between certain intensities of tem- 

 perature and flowering in certain plants, par- 

 ticularly in fruit trees of temperate regions. 

 Certain exotic ornamentals may live on from 

 year to year in certain localities and never 

 blossom. Some such may blossom in an 

 occasional warm season, but not produce 

 seeds, while the same species, in some shel- 

 tered and warmer spot in the same general 

 region may flower every season and even pro- 

 duce scanty or abundant seed. Some plants 

 may blossom only where the sun strikes them, 

 on the southern side, in the northern hemis- 

 phere. In a hedgerow, the spotwise blossom- 

 ing is often very noticeable and can readily 

 be traced to insolation. I have watched such 

 ft hedge of Laburnum in Berkeley, California, 

 in which the spots receiving the most sun 

 blossomed out a week or more earlier than 

 the rest. I have observed rows of Azalea cali- 

 fomica in the neighborhood of the Tosemite 

 Valley, largely shaded by tall trees, blossom 

 only in the spots where the sun penetrated to 

 them. Many such instances might be evi- 

 denced, but the resultant inference is the 

 same. Lloyd (1917) has recorded his obser- 

 vations on the " Critical flowering and fruit- 

 ing temperatures for Phytolacca decandra." 

 At Tucson, Arizona, this species produces 

 flowers and seeds in abimdance, but at Carmel, 

 California, a locality of decidedly lower tem- 

 perature maximum, it fails to do so, although, 

 otherwise, it grows well and apparently nor- 

 mally. Plants grown in a small glass shelter 

 »t Carmel, however, produced an abundance 

 of flowers, fruits and perfectly viable seeds. 

 In one or two instances single branches of 

 plants without the shelter, but in sheltered 

 positions, also bore seeds. As a result of 



