AGRICULTUKAL BOTANY. 223 



older plants were somewhat impaired by difficulty lii freeing them from foreign 

 materials, but apparently they contain a smaller percentage of amino nitrogen 

 than do the stems, 



A note on the significance of sugar in the tubers of Solanum tuberosum, 

 O. Butler (New Hampshire Sta. Sci. Contiil). 7 [1913), pp. 110-118, pi. 1, figs. 

 2). — A reprint of an article previously noted (K. S. R., 2!), p. 219). 



On the relation between the concentration of the nutrient solution and the 

 rate of growth of plants in water culture, W. Stiles {Ann. Bot. [London'], 

 29 (1915), No. 113, pp. 91-96).— Tho results of a study with rye and barley in 

 water cultures indicate that the variation over a fairly wide range of the con- 

 centration of the nutrient solution of rye and barley growing in water culture 

 produces i-elatively little effect on the amount of dry matter produced. Below a 

 certain concentration it is said there was a definite falling off in the rate of 

 growth. The concentration of the soil solution, as estimated by Cameron 

 (B. S. R, 26, p. 122), is said to be high enough to produce healthy plants. 

 Frequent changing of the nutrient solution of water cultures, it is claimed, 

 produces decidedly better growth of the plants. It is considered necessary to 

 calculate the probable error of the results obtained in experiments with water 

 cultures in order to determine the significance of differences between results 

 from different sets of cultures. 



An experimental study of the rest period in plants. — The summer rest of 

 bulbs and herbaceous perennials, W. L. Howard (Missouri Sta. Research Bui. 

 15 (1015), pp. 25, pis. 4).— This is a second report (E. S. R., 23, p. 526) and 

 relates to the summer rest of bulbs and herbaceous perennials. 



From results of experiments with ether and other agents as described, it is 

 concluded that most or all bulbous plants have a pronounced summer rest 

 period, which is difficult to shorten or to break during its earlier stages with 

 the means which pi'ove effective in case of woody plants, but it is believed 

 that this may be practicable by employment of temperatures not over 60" F. 

 after treatment. Desiccation followed by injection with ether and Knop's 

 solution, and combinations of these, seem to be the most effective treatments 

 tested for shortening the rest period. 



Experiments with a lai'ge number of species of herbaceous pei'ennial plants 

 showed that for most of these freezing was perhaps the best treatment for 

 forcing early growth, but its effects were not cumulative. In case of plants 

 already in leaf its effects were sometimes harmful, as were also those of 

 etherizing, which proved very stimulating in some cases. 



It is believed that several species of herbaceous perennials have a rest 

 period, but that they may be aroused by proper treatments, frost, desiccation, 

 and ether appearing to be the most effective agents. 



An experimental study of the rest period in plants. — Pot-grown woody 

 plants, W. L. Howard (Missouri »S7ff. Research Bui. 16 (1915), pp. 27, figs. 12).— 

 This is the third report of this series, giving results of more recent work than 

 that above noted. The author states that rest period studies with woody plants 

 can be as safely carried out with twigs 12 to 15 in. long as with trees or shrubs 

 growing in pots. It is held that the rest period and its interruption relates to 

 the bud itself rather than to roots, cambium, or any tissue of trunk or branches. 

 The roots of potted plants are not affected directly by the ether treatment. 



It is considered probable that dormancy of plants depends upon suspension of 

 enzym activity, awakening upon its resumption. It is thought that practically 

 all woody forms rest for a longer or shorter period of time, and that all can be 

 aroused by proper treatment, some more difficultly than others. Quickly respon- 

 sive species are considered to be in a state of enforced and unnatural rest, due 



S451°— No. 3—15 3 



