448 



here a few especially pertinent observations. Some of these consider the 

 question of light on the production of an intumescence. In this connection 

 Atkinson^ explains that increased turgescence in leaves will be produced by 

 repressed transpiration if the greenhouses are poorly Hghted. Actually, in 

 many cases, I found intumescences in the autumn and winter, because of 

 cool, cloudy weather, if the greenhouses had to be heated after the plants had 

 been brought in from outside. Trotter- states directly that half darkness 

 favors the formation of intumescences. Steiner'' also made the same 

 observation, but stated that they will form only in the first days of darkness, 

 so that one may conjecture an after effect of the former acti\ ity of the light. 

 This author observed also in Ruellia and Aphelandra, that the plants with 

 equal atmospheric humidity only formed intumescences for a few weeks 

 and therefore had adjusted themselves to the high degree of moisture. That 

 the abrupt transition from dry to moist air is actually the decisive factor is 

 shown by the renewed formation of intumescences, when the plants, after 

 having become adjusted to a dry atmosphere for three weeks are brought 

 again into moist air. 



Steiner found that no intumescences are jjroduced under water, as did 

 Kiister'' on ])()plar leaves which he had left floating on water or nutrient 

 solutions and in darkness as well as in light. Only when the illumination 

 was too great, this process was suppressed, probably as a result of increased 

 transpiration. In contrast to this, A^iala and Pacottet", in describing intu- 

 mescences on grape leaves in greenhouses, said tlie\- had determined by 

 direct experiment that intumescences are produced by the action of the 

 light in a moist atmosphere. They are produced only directly under glass. 

 The Missouri Botanical Garden makes a similar report. 



The most thorough experimental studies are Miss Dale's". She ob- 

 served with Hibiscus vitifolius, that the yellow and red rays are especially 

 effective in producing intumescences. Her experiments with potatoes are 

 especially instructive in regard to the action of sudden changes in the vege- 

 tative conditions. The plants were grown in a cold section of a greenhouse 

 and then set in a warm house at a temperature of about 2i°C., under a 

 brightly illuminated bell-glass. After 48 hours, the stem and the upper 

 side of almost all the leaves were covered with masses of pale green raised 

 spots. If the plants were then brought into dry air, the blisters shrivelled 



1 Atkinson, O. F., Oedema of the tomato. \\\\\\. C'ornell Agric. Exp. Station 

 1893, No. 53. 



- Trotter, A., Intuniescence.s I'os'liari dj Ipomea Batatas. Annali di Botanica 

 1904, No. 1. 



:■• Steiner, Rudolf, Wber Intumescenzen bei Ruelli formosa and Aphelandra 

 Porteana. Ber. d. Deutsch. Bot. Ges. 1905, Vol. 23, p. lOf). 



4 KUster, E., tjber experimentell erzeugte Intumescenzen. P.er. der Deutsch. 

 Bot. Ges. 1903, Vol. 21, p. 452. 



•' Viala et Pacottet, Sur les verrues des feuilles de la vif?ne. Compt. rend. 

 Acad. d. sciences 1904, No. 138. 



I' Dale, E., Investif?ations on the abnormal outgrowths or intumescences on 

 Hibiscus vitifolius. Phil. Trans. R. Soc. of London, ser. B. 1901, Vol. 194.— 

 Dale, E., Further experiments and histolog-ical investigations on intumescences, 

 with some observations on nuclear division in pathological tissues. Phil. Trans. 

 R, Soc. of London 1906, ser. B. Vol. 198. 



