on the green parts of Hibiscus vitifolius Linn. 207 



growths which all have some points of resemblance with those 

 on Hibiscus while at the same time they differ from them not a 

 little. But they are important because in all cases the conditions 

 of their formation seem to be identical with those in Hibiscus. 



The outgrowths occur on leaves, or, more commonly in shoots, 

 either of the current year or of the preceding year or years. In 

 all cases the sub-epidermal tissue is concerned. In leaves the 

 chlorophyll-bearing cells, in stems the cortical cells, especially 

 those lying between the bundles of bast, as far as the cambium 

 and sometimes even including the wood, are the parts which form 

 the swelling. 



In a leaf or young stem the sub-epidermal cells, in an older 

 stem the cells beneath the cork-layer, begin to form the outgrowth 

 by considerable elongation in a radial direction. In some cases 

 this elongation is accompanied by little or no cell-division, so that 

 the number of cells remains about the same. Sooner or later 

 these tubular cells always break through the epidermis, or cork- 

 layer, as the case may be, so that a wound is formed, by which 

 the plant is rendered liable to the attacks of parasitic plants and 

 animals. In many cases described by Sorauer and by Frank, 

 the tissues are affected as far as, and including, the cambium. 

 This inclusion of the cambium leads to a pathological development 

 of the wood which is formed subsequently. Thus all the tissues 

 in the stem are, or may be, included in the development of the 

 outgrowth, and serious malformations, accompanied by splitting, 

 are the result. 



In Hibiscus vitifolius, on the contrary, the outgrowth is much 

 more superficial since it either consists exclusively of the epidermis 

 or of the epidermis and the cells immediately below it. And, 

 since the layer of cork which cuts off the outgrowth forms an 

 efficient protection to the deeper cortical tissue, no wound is ever 

 formed, and no splitting takes place. The superficial tissues only 

 are affected and these but for a time, so that, after the outgrowths 

 have been cut off by cork, the stem simply continues its normal 

 growth. 



It would seem therefore as if the formation of outgrowths in 

 Hibiscus vitifolius were a response on the part of the plant to an 

 alteration in the surrounding conditions, a response which is in 

 some respects more of the nature of a variation than a disease. 



If, instead of the dry atmosphere which is most favourable to 

 the growth of the plant, damp air be substituted, transpiration is 

 checked. As a means of compensating for the reduced transpira- 

 tion, the plant stores the superfluous water, which it cannot get 

 rid of, in outgrowths on its stems and leaves. If the humidity is 

 only temporary, as is the case in the countries of which the plant 

 is a native, where there is an alternation of wet and dry seasons, 



15—2 



