AGRICULTURAL BOTANY. 319 



Sachs' ostimat(Hl rnto of nssiniilntion of loaves of sunflower, 16 mg. per square 

 (leeinieter i)er hour, is substantially correct. The calculation of the equivalent 

 intake of carlxtu dioxid from the increase of dry weight can only be considered 

 at present as a rough ai)proxiination, since there is too little known of the com- 

 position of the various i)roducts of 'assimilation. 



The carbohydrates of the snowdrop leaf and their bearing on the first 

 sugar of photosynthesis, .7. Parkin {Rpt. Brit. Assoc. Adv. tici., 1908, pp. 907, 

 908). — The author carried on experiments with the snowdrop {Galanthus niva- 

 lis) to -v^xtend knowledge regarding the sugars which appear as a direct effect 

 of pliotosynthesis. Thks plant was selected, as under ordinary conditions no 

 starch is formed in its mesophyll and the problem is not complicated by the 

 presence of maltose. If sucrose is present it is held that it could not have 

 originated from maltose. 



The author found, as a result of about 40 duplicate analyses, that the quan- 

 tity of sugar in the leaf is considerable, and that the amount in a single leaf 

 increases from above downward. At the same time the ratio of sucrose to 

 glucose and fructose diminishes. The proportion of sucrose to the hexoses 

 (glucose and fructo.se) decreases as the season advances. The percentage of 

 hexoses remains fairly constant while that of the sucrose fluctuates greatly, 

 increasing during the day and diminishing at night. Leaves darkened for 

 some days still contain a moderate quantity of sugar, and when reilluminatetl 

 they show a large increase of sucrose, while the amount of hexose undergoes 

 little alteration. 



The author believes that in photosynthesis the formation of sucrose precedes 

 that of the hexoses rather than that the converse takes place. 



The factors influencing photosynthesis in water plants, A. M. Smith {Rpt. 

 Brit. Assoc. Adv. Sci., 1908, pp. 906, 907). — By means of an apparatus which 

 maintains a current of water containing dissolved carbon dioxid passing at a 

 constant rate over a plant inclosed in a chaml)er, the author was able to study 

 the conditions of assimilation, such as carbon dioxid supply, temperature, and 

 light. These are held to be the actual limiting factors under the different con- 

 ditions of the experiments, and it is shown that when carbon dioxid is the 

 limiting factor, plants with an internal atmosphere (flowering plants) have 

 an advantage over those without it in being able to convert a higher propor- 

 tion of the carbon dioxid. No depressing effect of carbon dioxid on assimila- 

 tion could be detected up to a point when the supply was abt)ut one-third of 

 saturation, corresponding to an atmosphere containing 33 per cent carbon 

 dioxid. or from 30 to 50 times as much as occurs in ordinary tap water. 

 Water plants were found extraordinarily sensitive to external conditions, a 

 night in the laboratory considerably depressing assimilation, and a week's con- 

 finement under laboratory conditions reducing it to a very small amount. 



Color changes in flowers produced by controlling insolation, H. E. Rawson 

 (Rpt. Brit. Assoc. Adv. »S'ci., 1908, pp. 902, 903). — A brief account is given of 

 experiments carried on in South Africa in which the color of nasturtiums was 

 decidedly influenced by cutting oft' the rays of the sun by op.-ique screens at 

 certain intervals during the day. The experiments with dahlias and cosmos 

 indic.-ite that their coloration can be changed as readily as that of nasturtiums. 



Mutual interactions of plant roots, J. B. Dandeno {Rpt. Mich. Acad. ISci., 

 10 {1908), pp. 32-36). — Experiments are reported which were conducted to 

 ascertain information regarding the material excreted by roots and the inter- 

 actions of the roots of one plant upon another. The experiments wei'e divided 

 into two groui)s. For the first period the seedlings were grown until the radi- 

 cles had attjiined a length of 15 to 20 mm. The second period included the 

 growth up to about 4 weeks. 



