1900 | THE HAUSTORIA OF THE ERYSIPHEZ 157 
host-cell wall. At the point where the vesicle begins, this collar 
suddenly becomes thin and becomes continuous with the outer 
contour of the vesicle. The diameter of a mature haustorium 
proved to be approximately equal to the diameter of the mycelial 
thread. When the vesicle is young, De Bary says it has a very 
delicate wall, but an old haustorium has a colorless double-con- 
toured wall within which is minutely granular protoplasm, either 
homogeneous throughout, or consisting of a dense ball in the 
middle surrounded by transparent granular protoplasm. Incases 
where the haustorium is extremely old the contents consist of 
shining, oily masses. Not infrequently, if the epidermis to be 
penetrated is thick or if the penetrating tube ceases to grow, he 
observed that the haustorium does not enlarge into a vesicle, but 
is surrounded by a cone-shaped or knob-shaped protrusion of 
epidermal wall projecting into the cell. De Bary also examined 
grapes and grape leaves infested’with Oidium Tuckeri. He seldom 
found the haustoria normal in the fruit of the grape, but usually 
he found only the penetrating tubes surrounded by the cone- 
shaped ingrowths of the browned host-cell wall extending into 
the epidermal cells, as just described. Even in cells containing 
mature haustoria he found no great disturbance wrought in the 
cell wall, the cell protoplasm, or fluid contents. He frequently 
observed, however, in otherwise normal cells, that the haustoria 
are surrounded by thick, irregular masses of protoplasm belong- 
ing to the host-cells, which ammonia or KOH would remove 
sufficiently so as to allow the true haustoria to be seen. Gradu- 
ally, the browning observed on the exterior of the epidermis 
spread to the contents of the infested cells, but he did not 
observe such extreme browning as was described by Von Mohl. 
It is to be noticed that all of De Bary’s studies of the haustoria 
were made from the surface of the leaves. 
Biisgen (10) refers to haustoria in reporting his obser- 
vations on the effects of chemotropic and other stimuli upon the 
germinating tubes of fungi. He germinated conidia of Erysiphe 
communis from leaves of Polygonum aviculare on slides under 
Cover glasses. In some cases he used sections of infested leaves 
