1897 | “ BACTERIOSIS” OF CARNATIONS 203 
eased and healthy leaves, and which resembled in many respects 
the organism described by Arthur and Bolley as Bacterium dian- 
ti, the cause of ‘“‘bacteriosis.’’ Infection experiments were 
made with this and other organisms, but the disease was not 
produced in any case. 
From this work and the fact that no fungi or bacteria what- 
ever were found associated with the disease in its earlier stages 
we were led to look in other directions for the cause. 
RELATION OF APHIDES AND THRIPS TO THE DISEASE. 
Aphides—Early in the work our attention was called to the 
manner in which aphides attack the plant. A careful study 
revealed the fact that the insects in question were seldom if 
ever absent from plants, and that when present in limited num- 
bers they were capable of producing effects identical in every 
way with those described under the name of “ bacteriosis.” 
Studies of serial sections of spots produced by the aphides 
showed a breaking or laceration of the mesophyll cells, extend- 
ing from the epidermis to various depths into the leaf. Oedemic 
swellings start from these points, resulting eventually in the 
development of all the characteristic symptoms described. Col- 
onization experiments with the aphides were repeatedly made 
and it was found that the insects alone were capable of producing 
the disease and that neither fungi nor bacteria were present until 
the malady was well advanced, and in such cases not regularly 
nor constantly. In the colonization work it was found that the 
insects crawl between the young leaves on the growing shoots 
and do most of their work where they cannot be reached by 
tobacco smoke in sufficient strength to kill them. It was further 
found that it takes about two weeks for a puncture to become 
visible to the naked eye, appearing first as a minute translucent 
dot, accompanied by slight swellings of the tissues. Severe 
cases of the trouble were produced in perfectly healthy plants 
by colonizing the insects upon them, and the new growth of 
badly diseased plants was kept entirely free from the malady by 
eliminating the aphides and other puncturing insects. These 
