June 23,1923 
Disease Resistance to Onion Smvdge 
1029 
similar to that commonly observed in distilled water or on nutrient 
media. However, where red or yellow scale tissue was added to the 
drops distinctly abnormal germination occurred. In a large majority 
of cases, the spore sent out a germ tube, which usually acquired a length 
of only about one micron, when the wall at its tip either dissolvedfor 
ruptured and a portion of the cell contents exuded and collected i^a 
naked mass at the end of the very short and usually indistinguishable 
tube. Thus at the end of 12 to 18 hours most of the spores were to be 
found each with a naked mass of the cell contents adjacent to them. 
This feature is illustrated in figure i and Plate 3. For the purposeJof 
the present paper this condition is referred to as “rupturing"’ of l 3 ie 
germ tube, although the exact details of the process have not been worked 
out and it is realized that further study may necessitate another descrip- 
Fig. I. —Effect of water extract of outer onion scales upon spore germination of the smudge fimgus. Bits 
of dry scales of white, yellow, and red onions were added to drops of spore suspension in distilled waters. 
Note typical germ tubes and appressoria in the case of the white scale as compared with abnormal 
germination in the case of the colored scales. The abnormalities are of three types: (i) Ruptured germ 
tubes, (2) short, thick germ tubes, (3) swelling of spores without production of germ tubes. 
tive term. This phenomenon usually prevented further functioning of 
the spore. 
In a smaller percentage of cases there occurred other abnormal types 
of reaction, which may be divided into two general classes. The tet 
class includes those which will be referred to as “swollen spores.” In 
this group there is a marked swelling of the spores, usually at one end, 
with septation occurring at the limit of this enlargement (fig. i); no 
germ tubes are formed. In the second class, designated as having 
“abnormal germ tubes,” the tube grows fcr a short distance, is usually 
swollen at tlie tip or abnormally large in diameter, and never produces 
an appressorium (fig. i). 
The percentages of various types of germination obtained in the first 
experiment are recorded in Table V. The results were determined by 
counting several microscopic fields from each slide. It is to be noted 
that ruptured germ tubes occurred with a large majority of the spores 
where red or yellow scale tissue was added to the drops. Moreover, 
the spores reacted essentially alike to the red and yellow tissue. 
Numerous repetitions of this experiment yielded essentially similar re¬ 
sults. The data from one of these experiments are recorded in Table VI. 
