83 



The question as to the external conditions by the action 

 of whi«h intumescences are produced, has been repeatedly treat- 

 ed experimentally fSorauer, Dale.) They arise as a result of 

 (87) "excess of water", if the plants under experiment develop &n a 

 saturated atmosphere. According to Dale, simultaneous action 

 of light is necessary in the case of Hibiscus; no intumescences 

 have been formed under water. •*• According to Copeland, they may 

 be developed on tomato-leaves by forcing water into the branches. 



It is more difficult to answer the question as to what 

 factors determine. whether mesophyll or epidermis, ?/hether the 

 lower or upper oell layers of the leaf furnish the intumescence. 

 From the constancy ?/ith which the undermost mesophyll cells, 

 in E pilobium hirsutum . for instance, are enlarged, or the cells 

 of The under epideiSi's in Ipomea, the possibility" may be con- 

 sidered that Some constant structural peculairities of the leaf 

 release the stimulus only in certain cell-layers, or make pos- 

 sible a gro-yrth-reaction only for certain ones. Dale calls at- 

 tention to the fact that intumescences occur on both sides- of 

 the leaves of Hibiscus vitifolius , which bear stomata on both 

 sides, while Ipomea, with stomata occurring only on the under- 

 side of the Isaf develops intumescences only on this side. It 

 is indeed not improbable, that the formation of intumescences 

 is connected with the distribution of the stoniata. This is 

 pro^red also by the structures of the Vit^ceae, to be further 

 treated later (p. 90). But in no case has an explanation been 

 obtained by the discovery of these relationships which would 

 hold true for all cases, !Dhe examples cited above have already 



shown this. I ca^l attention once more td the intumescences on 

 the leaves of Ficus elastica illustrated in fig. 21, which are 

 produced by growth of the uppermost palisade cells, although, 

 as is well known, the leaves possess stomaba only on the under 

 side. In the majority of cases differences in the position 

 of the different cell-layers vifill presumably determine partici- 

 pation or non- participation in the intiunescence, Later v/e will 

 refer repeatedly to the fact that not all layers of the leaf- 

 tissue a-xe capable of reacting to the same stimulus in the same 

 way. 



Closer investigation is needed to prove how far the pro- 

 duction of intumescences is caused and favored by the treatment 

 of plants with p oisons, especially v/ith copper salts (compare 

 Sorauer) .* 



In connection with the intumescences, v/hich may be pro- 

 duced by the arrestment of transpiration or (according to Cope- 

 land) developed by the forcing in of water, a list of similar 

 formations may be mentioned in the following, corresponding to 

 developmentally and histologically. Haberlandt 3 developed in- 



1, That does not exclude the fact that occasionally the form- 

 mation of intumescences is incited by temporary moistening. 



2, Einige Beobacht. bei, d. Anwendung v. Kupfermitteln ge- ' 

 gen d, Kartoffelkrankh. Zeitschr. f. Pflanzenkrankh.l893,Bd. Ill, 

 p. 36, 



3, Ueb. experiment elle Hervorrufung eines neuen Orgajtis bei 

 Conocephalus ovatus Tree. Festchr. f. Schwendener, 1899, p. 104. 



