316 SUMMAEY OF CUREENT EESEAECHES RELATING TO 



Distilled water generally becomes alkaline if allowed to remain upon 

 leaves. Certain plants adapted to a moist climate may be made to take 

 in all the food necessary for growth through the leaves. Distilled water 

 used as a spray acts for a time as a stimulus to growth ; it may be that 

 it acts as a means of drawing from the plant surplus alkaline salts which 

 might become harmful if formed in too large quantity in the cells. 

 Rain-water may act as a stimulus in this way. 



Solutions, if applied to the surfaces of detached leaves, or to leaves 

 upon the plant, are generally absorbed, as shown by the increased content 

 of the ash. Solutions thus applied often stimulate part of the tissue to 

 an abnormal development. Solutions applied to the cut ends of leaf- 

 stalks are generally carried to the minute endings of the tracheides where 

 they kill the tissue either by drawing water from the cells into the 

 intercellular spaces, producing a translucent appearance of the tissue, or 

 by chemical action upon the walls of the cells, the protoplasmic membrane 

 or the protoplasm as a whole. The first determinable reaction after death 

 is alkaline even though the tissue be killed by an acid. 



The lithium test gives rise to error because the water ascends faster 

 than the lithium, and because the rate of ascent in the same leaf varies 

 as the length of the vein. 



A detached leaf is a living thing which may continue its functions, 

 to some extent, for several months after being detached from the plant. 



The food required by woody branches of Salix in the early growth of 

 spring is water, at this stage a nutrient solution was harmful. Water 

 and nutrient solutions are apparently absorbed through the buds. 



Since sea-water affects the atmosphere in such a way as to produce 

 an accumulation of rust upon iron greater than that produced in an 

 atmosphere under the influence of pure water, it is reasonable to 

 conclude that the atmosphere in the neighbourhood of the sea may 

 affect plants. 



Formic Aldehyde as a Food-stuff for Fresh-water Algse.* — R. 

 Bouilhac finds that formic aldehyde can be used by Nostoc and Anabmia 

 which are cultivated in a nutritive solution and exposed to an intensity 

 of light insufficient to allow of their decomposing carbon dioxide ; the 

 plants are thus obliged to obtain their carbohydrate food-stuff from an 

 organic source. 



A certain intensity of light is necessary to allow the Nostoc and 

 Anabmna to polymerise the formic aldehyde, and the minimum intensity 

 is very near that which is required for the assimilation of the carbon 

 dioxide of the atmosphere. 



Irritability. 



Influence of Light and Darkness on Plant-life.f — D. T. Macdougal 

 gives the results of experimental work extending over seven years and 

 including observations on a large variety of plants. These were culti- 

 vated in continuous darkness, control plants having been grown under 

 conditions otherwise the same, but in ordinary alternation of light and 

 darkness. The subjects of experiment include aquatics, creepers, climbers, 



* Cornptes Kendus, cxxxv. (1902) pp. 1309-71. 



t Mem. Now York Bot. Garden, ii. (1903) xiii. and 319 pp., 176 figs. 



