80 



remiryjL one of the aerenchyma formations described t>y 

 Lewakoffskil and Schenck {loc. cit.) in Lythrum salicaria . 

 Epilobiiam hirsutum. Lycopus europaeus . and many others. 

 Both authors ■ found produced on the immersed part of the 

 shoots a soft, spongy tissue the development of which Schenck 

 (83) followed more closely. The bark cells on the swollen pieces 

 of the shoots are enlarge abnormally and the products of the 

 cork meristem also have grovm out into long sacs, distended 

 radially, which leave large intercellular spaces open be- 

 tween them, just as in the bark cells;- essentially therefore 

 in the plants named, a similar tissue formation is caused by 

 contact with vjater as in our Ribes cuttings in moist air. 

 Schenck named the porous tissue, furnished Toj the cork mer- 

 istem, aerenohyma:-"the phellogen of the above swamp plants 

 can have two positions structurally, and the one or the other 

 will be developed according to the consistencjr of the medium. 

 ?/hat acts here as cause of the stimulation? It is not very 

 probable that the mere contact of the epidermis with water 

 may be considered as such; it should rather be supposed, that 

 the lack of 03cygen of the inner tissues reguirea the develop- 

 ment of aerenchyma by the cytoplasm, of the phellogen cells." 

 There can be no doubt in the case of the Ribes cuttings which 

 we studied, but'aht lack of air doBS not give rise to the 

 chahge of bark, and cork tissues; indeed the amount of air 

 furnished to the parts of shoots furrowed by the rifts is 

 evidently especially abundant a-nd the formation of the ab- 

 normally large distended cells is lacking in the immersed 

 pieces of twigs which are kept from a supply of air. The 

 similarity between our bark excrescences and the aerenchyma 

 tissues described by Schenck would therefore, be a purely 

 formal one« In the great similarity between lenticels and 

 bark excrescences, it would be advisable to keep' them sep- 

 arate from the typical aerenchyma tissues formed, according 

 to Schenck^ s conception, by respiratory necessity. A supple- 

 mentary testing 6f the conditions under which the cork mer- 

 istem of Lythrum, etc. , develops aerenchsnna might not be 

 superfluous • 



b. Intumescences. 



When the cell- out growths, v/hich in the case of Ribes and 

 others led to a total change of the surrounding tissue masses, 

 occur only in very limited are&s, small pustules are produced, 

 which we, with Sorauer, will designate as Intumescences . The 

 processes of growth by which they ^re produced are essentially 

 the same as in the case of the bark escrescencei? discussed 

 above, their production also presupposes the action of the same 

 external factors, only the size proportions and the habit of 

 growth of the excrescences differentiates it from them. Further, 

 excrescences vstoich we term intumescences prefer the primary 



1, Ueb. d. Einfl. d. Mediums auf die Form d. Pfl. Vergl. 

 Bot. Jahresber, 1873, p. 594. 



