154 BOTANICAL GAZETTE | MARCH 
Investigation received a stimulus from economic considera- 
tions, when, in 1845, a destructive grape disease appeared at 
Margate, England. Tucker, a gardener there, was led toa study 
of a mildew on the vines, because the spread of the fungus kept 
pace with the symptoms of disease. He published the results 
of his study in the Gardeners’ Journal of 1847. The mycelium is 
described as ramifying through the intercellular spaces of the 
host-leaves and as sending reproductive branches to the exterior 
through the stomata. Tucker believed the fungus was a parasite 
on the vines. He was aided in his investigations by Berkeley 
(3) who figured and described the fungus as a new species 
(Oidium Tuckeri). Berkeley repeatedly referred (4) to the 
hemi-endophytic habit of the fungus, and as late as 1886 
Worthington G. Smith (30) affirmed that the mycelium may 
sometimes be found on the interior of the leaves. If Berkeley's 
observations are correct, Oidium Tuckeri would seem to be related 
to Phyllactinia (p. 175) and to be distinct from the American 
Uncinula spirals. 
From England the disease spread to France and appeared at 
Versailles in 1848 (9). By 1851 it had spread all over Europe, 
causing much distress in vine-producing districts. Losses to 
owners of vineyards were so great that in France and Italy 
commissions were appointed to investigate the disease. Inde- 
pendently, Von Mohl (33) set for himself the task of determin- 
ing whether the fungus caused or followed the disease, since 
Robineau (25) had ascribed the disease to an insect. Von Mohl 
did not record his methods of investigation, except to state that 
he examined the interior of the fruit under a microscope (33, P- 
14). In this connection he noted the cracking of the larger 
grapes when covered with fungus. His search in the interior 
tissues of the fruit did not reveal the presence of the fungus 
there, so he concluded that the fungus produced its effects 
through the epidermal cells. Upon the epidermal cells of the 
young leaves, flowers, and fruit were to be seen, as soon 4S the 
fungus became visible, brown spots, which spread as the fungus 
_ Spread. Young fruit upon which the fungus appeared did not 
