INFECTION THROUGH NECTARIES. 



55 



have studied this phaseof the subject experimentally. In 1891 ,Waite sprayed pure cultures 

 of Bacillus amylovorus upon pear-flowers and obtained many cases of blossom-blight. 

 This was studied in all stages, from the first incipient multiplication of the bacteria in the 

 nectar to the destruction of the flower and the passage of the bacteria down the pedicel 

 into the stem. By protecting the flowers from the visits of insects by means of mosquito- 

 netting, this artificially induced blossom-blight was restricted to certain branches. This 

 particular experiment was made in an orchard in Kent County, Maryland, which was 

 remarkably free from natural blight and had been for years. In other experiments, not 

 in that orchard, Mr. Waite again produced blossom-blight on certain clusters of pear- 

 blossoms by infecting the floral nectaries and by allowing the bees to have free access to 

 these blossoms he succeeded through their agency in transmitting blight to other flower- 

 clusters on the same tree. One of these experiments took place on the grounds of the United 

 States Department of Agriculture, an isolated 

 tree previously free from blight being used for 

 this purpose. Bees were observed to visit the 

 infected flowers and, subsequently, flowers 

 on other clusters, which flowers afterwards 

 blighted. Some of these bees were caught, 

 their mouth parts excised, and cultures made 

 therefrom by means of poured-plates in Petri 

 dishes. Colonies obtained in this way closely 

 resembled the pear-blight organism, and inocu- 

 lations therefrom produced the disease in sound 

 pear-shoots, thus demonstrating beyond dis- 

 pute the actual presence of the pear-blight 

 organism on the mouth parts of the suspected 

 bees. 



Everybody connected with the plant 

 pathological work of the U. S. Department of 

 Agriculture at that time had knowledge of 

 these results. The writer, among others, saw 

 all of the experiments described and knows 

 that they were well done and that the above 

 brief outline can be accepted as an accurate 

 statement of what actually took place. 



In 1898 the writer produced Wakker's yel- 

 low disease of hyacinths on two occasions by 

 inoculating through the flowers, but not all of 

 the inoculated plants contracted the disease, 

 and nothing is known respecting the natural 

 occurrence of this disease as a result of nectarial 

 infection. The same year a soft white rot of 

 hyacinths, of the same type as Heinz's rot, was 



observed by the writer to originate in particular flowers and end in the destruction of the 

 plants. It is deemed probable, therefore, that in the field both of these diseases may some- 

 times begin in the floral nectaries and be distributed by nectar-sipping insects. The hya- 

 cinth gardens of Holland, where these diseases occur naturally, will afford a final answer 

 to this question. 



*Fig. 9. Marginal leaf-infections on cabbage (No. 400) obtained by atomizing on a pure culture of Bacterium 

 campestre, shaken up with sterile water. Inoculated Dec. 9, 1904. u, photographed Jan. 6, with transmitted light, 

 marginal halation being avoided by a close fitting paper screen which cuts out leaf-serratures. b, contact print made 

 Jan. 5 (lights and darks reversed). This is one of the plants that furnished material for the drawings shown in vol. I. 



Fig. 9: 



