204 Miss Bale, On certain outgrowths {Intumescences) 



and damp green-house to a dry 1 , open, and relatively cool position 

 in the open air resulted in a complete loss of outgrowths and a 

 vigorous development of the plants. On the other hand, change 

 to the cool, badly illuminated, and very damp Filmy Fern House 

 produced unhealthy conditions in the plant, without however 

 resulting in the formation of outgrowths. 



The conditions of illumination, moisture, and (during the 

 unusually hot summer) even of temperature, in the remaining 

 houses, were not dissimilar, and the plants grown in them did 

 not differ from one another essentially. In all the houses the 

 illumination was very much lessened by white-washing the side 

 windows and shading the roof with blinds. The Filmy Fern 

 House, which has a North aspect, whereas all the others look 

 South, was particularly dark and quite sunless. 



It would seem therefore as if the most important factors in 

 determining the formation or non-formation of the outgrowths 

 were moisture, light and temperature ; especially moisture and 

 light. Dry air and a strong illumination prevent the production 

 of outgrowths, while a moist atmosphere combined with strong 

 illumination and a sufficiently high temperature appears to 

 promote their development. 



The absence of outgrowths in the plant placed in the Filmy 

 Fern House seems to be explained by supposing that the plant 

 was so enfeebled by the very unfavourable conditions that it 

 had not the necessary strength to form outgrowths, but succumbed 

 without being able to adapt itself to its changed environment. 



These conclusions are in accordance with what might be 

 expected from our knowledge of the habitat of the plant. Trimen 2 

 says that Hibiscus vitifolius is common in the low country of 

 Ceylon, especially in the dry region. 



As to the nature of the outgrowths, the evidence so far avail- 

 able would seem to show that they are pathological. 



Kuntze 3 states that in certain Malvaceae, including some 

 species of Hibiscus, the epidermis is capable of swelling, and 

 sometimes its cells even divide, to form an aqueous tissue. 

 This swelling is promoted by the presence of mucilage. Each 

 epidermal cell may become as many as twenty times its original 

 size by the addition of water, which these cells can themselves 

 absorb directly. In the very delicate leaf of Hibiscus micranthela 

 the swollen epidermis on each side may be thicker than the green 



1 Note. During the past summer (1899), owing to a long-eontinued drought, 

 the air was particularly dry, more especially as, besides the absence of rain, there 

 was a great deal of sunshine and a prevalence of Northerly and Easterly winds. 



2 Trimen, Handbook to the Flora of Ceylon, 1893, Part I., p. 154. 



3 Kuntze, " Beitrage zur vergleichenden Anatomie der Malvaceae," Bot. Gent., 

 1891, pp. 198—200. 



