CHANGES OF COLOUR AND STRUCTURE OF FLOWERS. 45 



short a time to obtain a plant with all its flowers multi-spurred, but 

 already whole branches have been found with all the flowers structurally 

 altered in this way. It appears that if the same sunlight is removed for 

 three years a character of this kind can be fixed. The exact insolation 

 for producing multi-spurred flowers has been ascertained with consider- 

 able precision. When it was applied to a plant of Tropaeolum tuberosum, 

 with a view to obtaining such flowers, they sported at once, and I am able 

 to show you one of the 2-spurred flowers. Changes in the number and 

 form of the petals occurred, you see, as well ; but, what was still more 

 remarkable, the plant was then found to have no subterranean tubers. 

 It was potted and taken into the conservatory for the winter, and aerial 

 tubers began shortly to grow on the stems. The experiment was re- 

 peated last summer, and I have brought this plant for you to seethe two 

 aerial tubers growing from nodes three or four inches above the surface 

 of the ground (fig. 36). The plant of the previous year grew luxuriant 

 stems from its aerial tubers, and there are at the present moment 

 fifteen aerial tubers on these new stems. I am not without hopes that 

 sunlight will be able to convert T. majus into T. tuberosum, for I am 

 already able to show you how the entire leaf of the former has become 

 deeply dentated so as to approximate to the leaves of the latter. 



My specimens illustrate several other changes which have 

 been produced in Tropaeolum flowers, but I will only draw your 

 attention to one, which has been repeated a second time last 

 year in the open garden. Two blooms were produced together on 

 a single peduncle so as to unite into one flower-head, with a whorl 

 of eight petals — a form of fasciation recognized under the name of 

 synanthy. 



You may wish for a suggestion as to how the solar radiation at 

 different altitudes of the sun can effect such changes as these. I 

 suggest that the}' are traceable to the fact that rays of different wave- 

 length are not of the same efficiency in carbon-assimilation or in the 

 formation of chlorophyll. In the course of the day the absorption 

 by the atmosphere is always found to vary considerably ; it sifts out at 

 some hours those rays which it allows to pass freely at others. It is 

 not difficult to understand that such a system of screening as has 

 been described must interfere with metabolism, and by affecting the 

 actual formation of chlorophyll itself the transmission of the sun's 

 energy to the protoplasm must be subject to abnormal variations. Not 

 only Nasturtiums, but Dahlias, Poppies, Godetias, Chrysanthemums, 

 and Tomatos have been experimented upon, and have been proved to 

 be sensitive to the removal of sunlight in this way. By attending 

 to the connexion which seems to exist between aspect and colour, 

 the quantity of fruit obtained from the Yellow Tomato has been much 

 increased on two occasions. 



Flowers of Tropaeolum majus with two spurs were found and 

 described to the Botanical Society of Edinburgh in i860, and varia- 

 tions in the number and shape of the petals are far from uncommon. 

 Proliferation is often observed in various kinds of flowers, and it is by 



