107 



Jhe content of the Erineum hairs is extraordinarily rich 

 )S.?^° ^^^^' *^® vacuoles often contain red coloring matter 

 fTilia, Alnus, etc.). In Acer, Vitis and others only scanty 

 amounts of chlorophyll are developed. The club-like hairs 

 of a maple Erineura are very striking; in these an immense quan- 



i^^2 ^™^1^ starch grains are deposited, or smaller numbers 

 of often very composite starch grains lie next one another 

 like mosaic stones, filling the lumen of the cell. In other 

 hairs of the same Srineum form, fatty oil is found instead of 

 /-i-icN starch, which takes up part of the lumen of the hark in splen- 

 (115) did menisci or makes of the whole cell a filled oil-sac. Small 

 atarch grains and, isolated oil drops occur frequently in the 

 case of other Erineum forms,. In those forms which I have in- 

 vestigated, a cell nucleus may he found in each hair, whose 

 position, at least on the matured hairs, v/as not constant. I 

 discovered the nuclei in cluh-like hairs sometimes in the stalk 

 and sometimes in the head part. 



Simultaneously with the change of the epidermal cells in 

 the Erineum formation, the cell of the mesophyll also may some- 

 times be altered, They too gain at times in volume and not in- 

 frequently store up abundant starch. Generally their chloro- 

 phyll fades then. This co-operation of the mesophyll may be 

 recognized macroscopically by the fact that the leaf occasion- 

 ally appears to have heen pushed out into cuculli on the places 

 ii^^fected by the felt-gall. This warping always takes place in 

 such g^ wgcy that the Erineum turf lies on the concave side.* 

 The tissue structure of the mesophyll on the infected places 

 either rem&ins normal (fig. 39) or arrested development, be- 

 comes evident lea, the processes of differentiation, the meso- 

 phyll then remaining homogenous, (Compare fig» 38). 



Finally those gall forms Should he mentioned briefly , 

 whose abnormal hairs are multicellular, and those which are 

 produced not by a new formation of hairs, but by hypertrophy 

 of the normal trichome. Frank reports an "Erinetun" of the 

 last kind (loc, cit. p. 48) on Querous Aegilops . Similar form- 

 ations occur elsewhere also. 



Since Fee, we have become better informed concerning 

 "^^^ etiology 'of the Erinea and know that their formation is to 

 be traced back to the colonigation of the plants by Phytoptus 

 mites. Undoubtedly the stimulus, causing the abnormal growth 

 of the epidermal cells, comes from a poison which the gall in- 

 sects produce, concerning which nothing more is knov/n. The 

 substance given out by them aeems often able to filtrate from 

 one epidermal cell into another and thereby to stimulate those 

 cells to hair formation which were not directly infected by the 

 mites. If the mites affect the underside of a leaf, their 

 virus can penetrate the whole thickness of the leaf and incite 



1. Compare also Meyen loc. cit. p, 243, v/ho observed the 

 embossment of the leaf and traced it back to enlargement of 

 the single cells, 



2, Heger, Ueb, einige duroh Phytoptud hervorgerufene gal- 

 lenartigen Blldungen. Verhandl., D. wissensohaftl. Vereins, 

 Santiago 1895, Bd. Ill, p. 149, 



