18 THOMAS: INFECTION OF APIUM GRAVEOLENS 
INFECTION OF ETIOLATED PLANTS 
The effect of etiolation of the host upon infection has been 
tested in various ways. The first series of plants were kept in 
a dark room for nine days just preceding inoculation. Controls 
were kept on the greenhouse benches. The counts of spots per 
plant are shown in TaBLE VIII. This prolonged period in the 
TABLE VIII 
EFFECT UPON INFECTION PRODUCED BY ETIOLATING PLANTS FOR NINE DAYS IMME- 
DIATELY PRECEDING INOCULATION 
| 
Total No, A No, 
Plant No, t | 2 | 3 4 es I | oe Sins | Sones oat leaf 
ee Rete aa | 62 | 172 29| 63] 35!/ 30 50 8.0 
Control. ...........-..] 33 | 401 312| 2531 400 hs 72}. 3 04 16.7 
total absence of light materially changed the plants in a number of 
ways. The most noticeable changes were loss of chlorophyll, 
elongation of the petiole, and reduction in size of the leaflets. The 
reduction in leaf area, however, was plainly not commensurate 
with the difference in amount of infection. Neither can the 
suspension of photosynthesis be held entirely accountable for the 
less vigorous action of the parasite, in view of the various other 
changesin the host and in the light of the following further experi- 
ments. 
The second series of plants were ege in the dark room for 
three and one half days immediately following their removal from 
the inoculation chamber. The plants were not materially changed 
in appearance and it may be seen at once in TABLE IX that no 
TABLE 1X: .¢ 
EFFECT OF ETIOLATION FOR THREE AND ONE-HALF. DAYS FOLLOWING THE REMOVAL 
OF PLANTS FROM THE INCUBATION CHAMBER 
Plant No, I 2 3 4 5 6 Total No, No aeats 
leaves per le af 
a ees 422 163 313 | 584 403 565 | 48 , §0.9 
Controls ys.) | 623 | 368 495 350 | 342 | 382 AT: 54.4 
noteworthy variation was produced in the amount of infection 
as compared with the control plants. It was noted moreover 
a aS 
