280 ANNUAL, REPORTS OF DEPARTMENT OF AGRICULTURE. 



to which the plant is exposed which imdoiibtedly influences plant 

 behavior at different altitudes and also may be expected to be a 

 factor of importance in very high latitudes. For example, a large 

 group of plants which are typical biennials when exposed to the 

 usual summer condition in lowlands of relatively long days in 

 conjunction with coinparatively high temperatures are caused to 

 behave as annuals where subjected to a combination of long days 

 and a somewhat lower temperature level, a relation such as wovild 

 usually obtain at high altitudes. Lower temperatures alone, how- 

 ever, do not accomplish this result. On the other hand, the combina- 

 tion of a long daylight period and a relatively cool temperature 

 affects some plants unfavorably. Another feature of the photo- 

 periodic response, of special interest and significance, is the fact 

 that the formative action of the light period may be sharply local- 

 ized. Thus, in the case of cosmos, by appropriate exposure of 

 different portions of the stem to different day lengths, flowering 

 may be induced in either the apical or the basal portions or even in 

 the middle zone, while the remainder of the stem continues in the 

 vegetative state. Investigation has revealed that the formative 

 action of the light period is associated with definite change in the 

 hydrogen-ion concentration of the cell sap. With the group of short- 

 day plants, abrupt change from long-day to short-day conditions 

 results in a sudden and decided decrease in aciditj', which occurs 

 three to five days after the change in the illumination period has 

 been made. This phenomenon is believed to mark the transition from 

 the vegetative to the reproductive tj'^pe of activity. Abrupt change 

 from a long to a short daylight period also results in a prompt and 

 well-defined increase in total soluble carbohydrate in the cell, accom- 

 panied by changes in distribution of soluble carbohydrate between 

 monosaccharid and polysaccharid. 



SOIL BACTERIOLOGY. 



Nitrification of green manures. — Green manures of different kinds 

 and of different ages applied in different quantities have been tested 

 in the field, in the greenhouse, and in the laboratory. In the green- 

 house experiments their effect upon crop production was clearly 

 noticeable for four years. In a heavy clay soil of little natural pro- 

 ductivity, the nitrogen availability varied between 30 and 80 per cent, 

 but in a very fertile soil higher returns were obtained. Especially 

 with small applications of manure, more than 100 per cent of the 

 nitrogen applied was frequently recovered in the crops; that is, the 

 activities of the soil organisms became so intense under the influence 

 of the manures that the humus nitrogen present in this soil was more 

 rapidly nitrified than that in the unmanured soil. Accordingly, nitri- 

 fication tests made in the laboratory with the different green manures 

 yielded results which in some cases agreed well with the nitrogen 

 efficiency recorded in the greenhouse, but in other cases they were 

 much lower, again indicating that more humus nitrogen was used 

 by the manured plants. The field tests showed, in addition, that 

 nearly the same crop increases may occur if the gi'een parts of the 

 legumes grown for green manuring are removed, so that only stubble 

 and roots are left. 



