( 179 ) 



had nol hindered these leaves at all in their normal development. 

 Only scale-insects and other animals had been prevented from settling 

 on the leaves with the formerly described result. 



Similar tumours as the yellow, thickened leaf-tips of Gnetum 

 Gnemon really are, have also been repeatedly observed with other 

 plants and described under the name of "yellow specks" (Gelbflec- 

 kigkeit), oedemata or intumescences. The word "Intumescentia" was 

 introduced into phytopathological nomenclature by Sorauer with the 

 definition 1 ): "Intumescentia" sind "diejenigen Erscheinungen, die das 

 gemeinsame Merkmal haben, als kleine knötchenförmige oder drüsige 

 Auftreibungen der Blatter aüfzutreten, die meist an diesen Stellen 

 gelb verfarbt erscheinen and eine aussergewöhnliche Zellstreckung 

 ohne wesentliehe Zelh ermehrung zeigeiv". That the thickened leaf-tips 

 of Gnetum Gnemon are not indeed "kleine Auftreibungen" and do 

 present "wesentliche Zellvermehrung" need not necessarily prevent 

 us from counting them among the intumescences, since as well very 

 large 2 ) or mutually coalesce] 1 1 ') as typically hyperplastic *) intumes- 

 cences have been described for other plants. 



We cannot now deal with the very divergent views of different 

 investigators about the cause of the formation of intumescences; we 

 will only mention that in most cases it has been stated that a high 

 temperature and great humidity of the air are essential factors. 



Experiments enabled me to form an idea about the character of 

 the stimulus exerted by the scale-insects on the tissue of the leaf of 

 Umi', it Gnemon, on which the formation of the intumescences is 

 the reaction. After 1 had tried artificially to produce intumescences 

 in leaves by mechanically wounding them in all sorts of ways and 

 treating them with poisons, without obtaining the desired result, I 

 arrived at the conclusion that either my method of wounding, com- 

 pared with that of the scale-insects, was too coarse or that the 

 insect injected some stimulating substance into the leaf. In order to 

 settle these points the following experiments were carried out: 1). In 



1 ) P. Sorauer, Die symptomatische Bedeutung der Intumescenzen (Bot. Zeitg. 

 48 Jahrg. 1890. p 241). 



2 ) H. v. Schrenk, Intumescences formed as a result of chemical stimulation. 

 (Missouri botan. garden. 16th a uu. report. 1905. p. 125). 



3 ) Miss G. E. Douglas. The formation of intumescences in potatoplants. (Bot. 

 Gazette Vol XLUI. 1907. p. 233.) 



4 ) E. KiisTER, Uber experimentell erzeugte Intumescenzen. (Ber. deutsch. bot. 

 Ges. Bil. XXI. 1903. pag. 452). P. Sorauer, Ueber Gelbfleckigkeit. (Forsch. a. d. 

 Geb. d. Agiik. Phys. h. v. Dr. E. Wollnyt. Bd. IX. 1886. pag. 387). and Intumescenz 

 bei Solanum fJoribundum. (Zeitsclir. f. Pllanzenkraukh. Bd. VII. 1897. p. 122). 



