1G Miss E. Dale. On ike Abnormal Outgrowths or 



" Further Investigations on the Abnormal Outgrowths or Intu- 

 mescences in Hibiscus vitifolius, Linn. : a Study in Experi- 

 mental Plant Pathology." By Elizabeth Dale. Communi- 

 cated by Professor H. Marshall Ward, F.B.S. Eeceived 

 November 22, 1900— Eead February 7, 1901. 



(Abstract.) 



During the summer of 1899 some preliminary experiments were 

 made in order to investigate the conditions determining the formation 

 of certain outgrowths of which the structure had previously been 

 examined.* These outgrowths consist chiefly of greatly enlarged and 

 multiplied epidermal cells, with very thin walls ; but the underlying 

 parenchyma is often also affected. The cells concerned always lie 

 immediately around a stoma, so that the guard-cells are lifted up as 

 the outgrowth developes. The distribution of the outgrowths is there- 

 fore dependent upon that of the stomata, and they are pathological in 

 origin and nature. 



This year (1900) further experiments have been undertaken, which 

 •confirm and extend the conclusions suggested by the earlier work, and 

 which show that we have here a clear case of a pathological pheno- 

 menon brought under control. 



The plants used were chiefly Hibiscus vitifolius, but some observa- 

 tions were also made on Ipornea Woodii. 



The experiments were designed to test the effects of moisture and 

 light in inducing the formation of the intumescences, but they also 

 served to show the influence of temperature. Most of them were 

 made in the open air, as the outgrowths always arise on plants growing 

 in a greenhouse. 



I. In order to test the effects of moisture in the air and in the soil, 

 plants were kept with their shoots in dry or moist air, and their roots 

 in dry or damp soil. Various combinations of dry or damp air or soil 

 were used, with the result that outgrowths were always formed in 

 damp air (provided there was sufficient light and heat), whereas damp 

 soil had no effect. 



II. The effects of light were tested by growing plants in white light 

 of varied intensity, and under glass of different colours. Outgrowths 

 were developed under clear and whitewashed glass, and under red 

 and yellow glass, but not under blue or green glass, nor in poor light, 

 and never in darkness. 



III. Observations as to the influence of temperature showed that, 



* Dale, " On Certain Outgrowths (Intumescences) on the Green Parts of 

 Hibiscus vitifolius, Linn.," ' Proe. Carnb. Phil. Soc.,' vol. 10, Part 4. 



