August 27, 1920] 



SCIENCE 



189 



temperature readings under the different con- 

 ditions, Lloyd came to the conclusion that 

 raising the temperature not over 5° F. would 

 be sufficient to produce normal flowering at 

 Carmel. M. Moebius (1897) has treated of 

 the matter of temperature in his " Beitrage 

 «ur Lehre der Fortpflanzung der Gewachse " 

 iind brings forward many authenticated cases 

 of the effects of changes of temperature on 

 the flowering and fruiting habits of plants. 

 He calls attention to the fact that plants pro- 

 Tided with effective methods of vegetative 

 multiplication, such as the members of the 

 Lemnacese, may occur in abundance in cooler 

 legions, such as Central Europe, but seldom 

 or never (Wolffia) fruit, while they bloom and 

 fruit abundantly in warmer regions where 

 they are equally common. The difference in 

 temperatiu-e in these cases is partly of greater 

 intensity, although presumably not consider- 

 ably, partly also of duration of the higher 

 intensity. 



It seems to me that it is this narrow 

 interval of temperature which separates the 

 carrying through of reproductive processes 

 from their inhibition, that is indicated by 

 correspondingly narrow temperature interval 

 between the isotheres and isocrymes which 

 seem to delimit so accurately the different 

 floras from one another. From the physio- 

 logical point of view, there seems to be indi- 

 cation that the optima of effective reproduc- 

 tion which makes for persistence in distribu- 

 tion, lie within an interval of 5° C, an 

 interval surprisingly narrow. The controll- 

 ing influence of this narrow interval, however, 

 so far as the persistence of the various species 

 in any zone or zones is concerned, seems well 

 substantiated by the various tabulations and 

 critical examination into seemingly excep- 

 tional cases which I have made and published 

 elsewhere. The overwhelming majority of the 

 knov^n marine algse of the world are recorded 

 from only one zone. A considerable number 

 are said to occur in two zones, a very few in 

 three zones and a very small percentage in 

 four or flve zones. It seems, therefore, fairly 

 cei'tain that the normal interval is one zone 

 of 5° C. amplitude and that the invasion of 

 other zones than the normal is due to the 



existence in the invaded zones of temperatures 

 of the same intensity and duration found in 

 the normal zone. This has been shown in a 

 sufficient munber of cases to indicate that it 

 is to be looked for as a general rule. 



There is another interval besides that 

 mentioned above, which has more or less to do 

 with the life, normal and invading, of any 

 particular zone and that is the interval of 

 amplitude of seasonal variation in tempera- 

 ture in each zone. There may be certain por- 

 tions of the tropical zone in which there is 

 little, if any, seasonal change of temperature. 

 In certain portions of the oceans, free from 

 (furrents of a strongly influencing nature, the 

 isocrymes and isotheres 5° C. apart are very 

 nearly superposed and it seems logical to as- 

 sume that this seasonal interval is normal. 

 The extreme interval in portions of zones 

 thus affected is, therefore, 10° C. in ampli- 

 tude, the interval between extreme mean 

 maxima and mean minima estimated from 

 monthly variations. This interval, viz., 10° 

 C, may be assumed to be the interval of 

 optimum temperatures for persistence and in- 

 cluding all actively vital processes of the par- 

 ticular species normal to any zone. There 

 are regions in some zones, however, where the 

 mean seasonal variation alone amounts to 18° 

 or 20° C. It is imdoubtedly a fact that where 

 the seasonal interval is large and particularly 

 where it is much greater than 5° C, the 

 species normal to the zone pass the colder 

 portion of the season in a state of quiescence, 

 or rigor, either in the vegetative or in the 

 seed or spore stages of development. In the 

 ooldar seasons of any region of a zone suffer- 

 ing a considerable seasonal interval, the in- 

 vading 8i)ecies from a lower zone are to be 

 found in vegetative and reproductive activity 

 and pass into a condition of quiescence when 

 the temperatures characteristic of the zone 

 prevail, a sort of heat rigor. As a result of 

 the extreme seasonal variation in temperature 

 of the northeastern coast of North America, 

 for example, Ascophyllum nodosum, one of 

 the rockweeds or Fucacese, whose normal zone 

 is the region of Greenland in the upper boreal 

 •one and where it develops its vegetative body 



