(79) 



7& 



same ei^crescences, as are found in the parts in conict with 

 the water. V. Tubeuf and Devaux have agreed that it is the 

 vapor from the water, playing about the lenticels, which in- 

 cites the cells to hypertrophy- Contact with water in a 

 liquid state is therefore not necessary, it is even suffi- 

 cient to bring pieces of twigs into an atmosphere, saturated 

 with TTapor, m order to produce lenticel-excrescences. 



Although in willow cuttings and in other species the 

 lenticels grow out more luxuriantly under water than in moist 

 air, there arise above and under the water excrescences almost 

 equally pronounced. Ihere are, however, a number of plants 

 on whose cuttings the fommation of the excrescences takes 

 place more quickly and abundantly in moist air than under 

 water. Indeed cases are not Eare, in which the excrescences 

 under water are entirely or almost entirely absent, but are 

 formed abundantly by the action of water vapor. Contact with 

 water in a liquid state arrests here the development of the 

 aerenchyma-like tissue. The difference between the moistened 

 and unmoistened parts of cuttings of Catalpa syl-ingaefolia is 

 very evident. These cuttings form white masses only in moist 

 air. Cuttings of syringa and others act similarly. Excres- 

 cences is omitted further under water in the root-lenticels 

 of different varieties of Acer, while their tissue hyper- 

 trophies unusually actively in moist air. Those lenticels 

 of the potato tubers are still 'to be mentioned, which form 

 lenticel-excrescences after having been kept several weeks in 

 moist air, but never under v/ater, and many others, 



I think the supposition is correct, that in the cases 

 mentioned, the excrescence of the lenticel tissue cannot 

 occur under the surface of the water on account of completely 

 suspended transpiration and deficient supply of oxygen. I 

 am supported in this assumption by observations on cuttings 

 of Syringa, Evonymus and others, in which the lenticels often 

 grow out especially abundantly near the wound-surfaces,- sup- 

 posedly because the supply of air creates the most favorable 

 conditions. 



It is of no consquence vi^hat external factors are decis- 

 ive in the omission of the lenticel-^excrescences under water. 

 In any case, the instances described make it scarcely prob- 

 able, that the aerenchyma-like lenticel tissues are of signi- 

 ficance for the plant, in that their cell connection, with 

 its abundant interstices, makes the breathing of the plants 

 easier even with a more difficult supplying of oxygen, as 

 Schenck assiimes with Jussiaea etc. In many cases, the afore- 

 said excrescences are produced where there is no lack of air; 

 indeed in the case of many plants, their production seems to ' 

 presuppose an abundant aupply of air. The rejection of 

 Schenck* s explanation will be forced upon us also by a con- 

 sideration of the bark excrescences described baiow,w.7hich 

 correspond in more than one v/ay with the lenticel-excrescen- 

 ces already described. 



1, Apparently different varieties of potatos act different- 

 ly; at least, I have often vaiiily endea,vored to obtain lenti- 

 cel excrescences in moist cultures of tubers, although in' 

 other cases, under apparently similar external conditions, 

 their formation took place very abundantly. 



