September 15, 1922] 



SCIENCE 



313 



gratifying exception. It stands, indeed, at the 

 very apex of all the work that has been done 

 upon the Coccidae. 



It is not that "The Coeeids of Ceylon" is 

 entirely free from defects. The fact that its 

 preparation has extended over more than a 

 quarter of a c-entury precludes this, for since 

 it was begun there have been radical changes 

 in our methods and in our standards as well. 

 Yet throughout it has always stood fully 

 abreast and even in advance of the best con- 

 temporaneous work. Above all, the student, 

 turning to its pages, can identify with relative 

 certainty the species with which he may be 

 dealing. With this much rendered possible, 

 criticisms of any other features are but sec- 

 ondary. It is a splendid work, beautifully 

 illustrated, well arranged and well printed. To 

 its author all entomologists, whether economic 

 or not, who are interested in the scale insects 

 are under an obligation that can but illy be 

 repaid. For the work has been a labor of love, 

 its author's recompense the pleasure in its ac- 

 complishment. 



With technical criticisms, of which there are 

 some, I am not here concerned. Nor is it nec- 

 essary to deal with the scope of the work, for 

 practically all entomologists are familiar with 

 this from the earlier parts. It is my desire 

 simply to call attention to the appearance of 

 the final part and to congratulate the author 

 upon the completion of a huge task well done. 

 Its completion clinches his hold upon a posi- 

 tion that has really long been his, that of the 

 foremost student of the Coccidse. 



G. r. Tereis 



Stanford University, Cahp. 



SPECIAL ARTICLES 



PHOTOPERIODISM OF WHEAT; A DETER- 



.MINING FACTOR IN ACCLIMATIZATION 



Gaener and AUard (4), working with several 

 species of plants, found that normally a plant 

 could attain the flowering and fruiting stage 

 only when the length of day was favorable, and 

 suggest the tei-ms photoperiod and photoperiod- 

 ism to designate the favorable length of day 

 and the response of a plant to the relative 

 length of day and night. They conclude that, 



varying with species and variety, there is a 

 critical photoperiod essential for the initiation 

 of the fruiting stage of each plant, and that 

 when this critical photoperiod does not oceui- 

 the plant tends to remain vegetative. 



In a preliminary experiment, the writer has 

 found that a proper adjustment of the daily 

 exposure to light, independently of tempera- 

 tui-e, will control the type of growth in the 

 winter wheat plant and that by regulation of 

 this factor it is possible to induce the jointing 

 and the heading stages irrespective of season. 

 In addition, this experiment has shown that 

 there is a minimum stimulating photoperiod 

 for the control of each of these stages of growth 

 in the winter wheat plant, that for the succeed- 

 ing stage not being the same as that for the 

 preceding, and each photoperiod being, there- 

 fore, within certain limits critical for the stage 

 concerned. 



Although factors governing habits of growth, 

 the distribution and the production of wheat 

 have been the subject of many studies, the liter- 

 ature available has not revealed that any have 

 ever considered, beyond the generalizations of 

 Garner and Allard, the factors of photoperiod- 

 ism as having a deciding influence. Circum- 

 stantial evidence, however, is available, which 

 on analysis clearly indicates that these factors 

 are important both with winter and with spring 

 wheats. Grantham (5), Jardine (6) and 

 Seivers and Holtz (11) have shown the ten- 

 dency of winter wheat to a vegetative type of 

 fall growth and have emphasized that the 

 amount of this growth is dependent on time 

 of seeding and available fertility. Gaines (10) 

 and Neilson-Ehle (7) have found, in certain 

 localities of the north temperate zone, the win- 

 ter character to be inheritable as a simple Men- 

 delian major. The northern limits of the 

 winter wheat belt in the United States bear- a 

 signiflcant relation to the northern limits of 

 an active growing season of 150 days (1, 2). 

 Smith, Eoot and Blair (3, 8, 12, 13, 14), in 

 statistical studies of data from Ohio, found 

 the dominant weather factor for winter wheat 

 difficult to determine, but all agreed that the 

 month of March was the critical period dming 

 which the effects of snowfall and temperature 

 were later most reflected in condition and finally 



