66 
way reach the apex of growth, finally come to development in the 
heads of the grain; all others fail. 
With this, we come to the penetration of the smut germs into the host- 
plants, so often vainly looked for until the investigations of Kiihn and 
Wolff threw additional light upon the subject, and till Kiihn proved 
the penetration into the young seedlings, especially in the vicinity of 
the root node. Wolff later announced and represented in his drawings 
the penetration exclusively into the sheath leaf. Both observers in 
their investigations had naturally worked only with smut spores ger¬ 
minating imperfectly and irregularly in water. 
For my observations I first began with very young seedlings. As 
soon as the plumule appeared (and the roots usually preceded this by a 
day or two) these seedlings were laid free on the earth, sprayed with 
the atomizer, and then examined after several days’ maintenance in 
suitably damp air. From all parts, from the apex to the root node, pieces 
of the epidermis were removed carefully and their surface examined for 
places of penetration. These were not to be found until the third day 
and were to be seen with most certainty on the fourth da} 7 ; later they 
became gradually obscure. The spots at once attracted attention by 
a distinct hole in the epidermis. Beneath and inward from this hole, 
which was often of considerable size, extended always the intruded 
germ tube which had already grown crosswise through the superficial 
cell layers and disappeared with its apex in the deeper tissues. The 
influence of the nutrient material inside the cells of the host plant pro¬ 
duced a marked effect on the germ tubes. The tubes here increased 
visibly in thickness and in vigorous appearance, and already in the 
deeper optical sections showed branches, which only very seldom ap¬ 
peared in germinations of the conidia in exhausted nutrient solutions. 
In favorable preparations portions of the surface were found which 
appeared as if riddled by drill-holes and were completely permeated by 
the numerous ingrown germ tubes to a degree not possible to be observed, 
even approximately, with infective material previously employed. 
The more recent the places of penetration, the easier it was to see the 
superficial conidia in direct connection, through the epidermal opening, 
with the germ tube which had penetrated into the surface cells. After 
a time this picture lost in distinctness, in proportion as all parts of the 
fungous germ lying on the outside became empty and transparent and 
only the penetrated fungous thread bore coutents. Still later the hole 
at the place of penetration disappeared and the germ threads in the 
outer cells lying near the place of penetration were transformed in’o 
delicate, empty threads, still to be recognized as fungous threads, ouly 
by the deeper union with normal portions of the tubes. I am inclined 
to believ r e that these rapid changes of the penetrated fungous threads 
take place because of the further growth and consequent stretching of 
the tissue of the seedlings, which were always infected in their earliest 
stages, long before they were full grown, and consequently before theit 
