Science of Gardening. 679 



(From a Paper by Dr. Daubeny.) — " The objects of the experimental en- 

 quiries, of which the author gives an account in this paper, were, in the first 

 place, to ascertain the extent of the influence of solar light in causing the 

 leaves of plants to emit oxygen gas, and to decompose carbonic acid, when 

 the plants were either immersed in water, or surrounded by atmospheric air. 

 The plants subjected to the former mode of trial were ^rassica oleracea, 

 Salicorniaherbacea, i^ucus digitatus, T^ussilago hybrida, Cochlearia Armoracea, 

 ilientha viridis, i?heum Rhaponticum, -^'llium ursinum, and several species of 

 Gramlne^. Geraniums were the only plants subjected to experiment while 

 surrounded with atmospheric air. Comparative trials were made of the action 

 on these plants of various kinds of coloured light, transmitted through tinted 

 glass, of which the relative calorific, illuminating, and chemical powers had 

 been previously' ascertained ; and the results of all the experiments are re- 

 corded in tables; but no general conclusion is deduced irom them by the 

 author. He next describes a few experiments which he made on beans, with 

 a view to ascertain the influence of hght on the secretion of the green matter 

 of the leaves, or rather to determine whether the change of colour in the 

 chromule is to be ascribed to this agent. The third object of his enquiries 

 was the source of the irritability of the Mimosa pudiea, from which it ap- 

 peared that light of a certain intensity is necessary for the maintenance of 

 the healthy functions of this plant; and that, when subjected to the action of 

 the less luminous rays, notwithstanding their chemical influence, the plant 

 lost its irritability quite as soon as when the light was altogether excluded. 

 He then examines the action of light in causing exhalation of moisture from 

 the leaves ; selecting dahlias, Helianthus annuus, Sagittaria sagittifolia, and 

 the vine. From the general tenor of the results of these and the preceding 

 experiments, he is inclined to infer that both the exhalation and the absorp- 

 tion of moisture in plants, as far as they depend on the influence of light, 

 are affected in the greatest degree by the most luminous rays ; that ali the 

 functions of vegetable economy, which are owing to the presence of this 

 agent, follow, in this respect, the same law ; and that in the vegetable, as well 

 as in the animal kingdom, light acts in the character of a specific stimulus. 

 The author found that the most intense artificial light that he could obtain 

 from incandescent lime produced no sensible effect on plants. 



" The latter part of the paper is occupied by details of the experiments 

 which the author made with a view to ascertain the action of plants upon the 

 atmosphere, and more especially to determine the proportion that exists be- 

 tween the effects attributable to their action during the night and during the day; 

 and also the proportion between the carbonic acid absorbed, and the oxygen 

 evolved. His experiments appear to show that at least 18 per cent of oxygen 

 may be added to the air confined in a jar by the influence of a plant contained 

 within it. He also infers that the stage of vegetable life at which the func- 

 tion of purifying the air ceases, is that in which leaves cease to exist. The 

 author shows that this function is performed both in dicotyledonous and in 

 monocotyledonous plants ; in evergreens as well as in those that are deciduous:; 

 in terrestrial and in aquatic plants ; in the green parts of esculents as well as 

 in ordinary leaves ; in algae and in ferns as well as in phanerogamous fami- 

 lies. Professor Marcet has shown that it does not take place in -Fungi." (^Lon- 

 don and Edinburgh Philosophical Magaziyie, May, 1836, p. 415, 416.) 



On the Colours of Flowers. — A curious essay on this subject, entitled 

 Die Farben der Bluthen, was published last year at Bonn, by Dr. Macquart, 

 from which we insert the following abstract of the results obtained : — 1. All 

 flower-leaves are originally green in the bud. 2. Chlorophyll (the green leaf) 

 contains no nitrogen. 3. All the tints of flowers are produced by two 

 colouring matters. 4. These colouring matters are produced by the action 

 of the living principle upon Chlorophyll. 5. When water, or its elements, 

 are removed from Chloryphyll, Anthokyan (dark blue flower) is formed. 6. 

 Anlhokuan is the colouring matter in blue, violet, and red flowers. 7. By the 



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