34 



BACTERIA IN RELATION TO PLANT DISEASES. 



Some of his experiments showed that the bacteria were carried over from seeds to 

 seedlings. On the surface of the latter they were found in much greater numbers than on 

 the seeds, particularly if the seedlings grew in closed dishes where the air was moist and 

 dew often appeared on their surfaces. The occurrence of the same bacterial forms on the 

 surface of mature leaves and stems suggests the way in which seeds and fruits become 

 contaminated. 



The nutritional requirements of his yellow and red species appear to be very simple, 

 since they were able to obtain their carbon food and nitrogen food from many different 

 substances. B. fluorescens and B. putidum were more exacting in their requirements. 



Fig. 4 shows masses of bacteria growing between the petals of the unopened flower 

 of the hothouse carnation in what the writer has called the gum-bud disease of the car- 

 nation. They are seen to be entirely outside of the tissues. Subsequently the petals 

 withered and the tissues were penetrated. At first the writer thought he had discovered a 

 genuine bacterial disease, but further study indicated that the growing together of the 

 petals on which depends the inability of the blossom to open normally, is the real cause of 

 the disease and precedes the occurrence of the bacteria. The cause of this fusion of parts 

 normally separate is unknown. 



In 1890, in the Annales of the 

 Botanic Garden of Buitenzorg, in a 

 paper on the flower buds of Spathodea 

 campanulata, Dr. Treub mentions the 

 fact that various bacteria occur nor- 

 mally in the liquid secreted inside of 

 the closed calyx. His statement is as 

 follows : 



The relatively large quantity of or- 

 ganic product [in the execreted fluid] ex- 

 plains the very curious fact, that normally 

 colonies of different micro-organisms de- 

 velop in the liquid of the pitchers of the 

 Spathodea without appearing to injure in 

 any manner by their presence the floral 

 organs in the process of development. 

 The introduction of the microbes produc- 

 ing these colonies may take place in two 

 different ways : first, they may date from 

 the time when the very young calyx is 

 still open ; then, they may insinuate them- 

 selves later into the narrow canal at the 

 summit of the pitcher and thus in the end 

 arrive at the liquid. I am inclined to 

 believe the second mode of introduction 



is the more frequent. In view of this fact it is not astonishing that the liquid contents of the perianth 



of the Spathodea campanulata is more or less putrid and ammoniacal. 



In 1897, in a long paper on the Hydatodes of the blossom buds of some tropical plants, 

 Mr. S. H. Korrders, in the same Annales, also refers to the "constant occurrence of bacteria 

 or fungus threads in the interior of water calyces. " He mentions bacteria as occurring in 

 the flower buds of Spathodea campanulata, Clerodendron minahassae, and Kigelia pinnata. 

 In the flower buds of other plants he found fungi. So far as he was able to observe, only one 

 fungus species occurred in one sort of water-calyx plant, although one would naturally 

 expect mixtures. In case of bacterial growths the reaction of the fluid inside the calyx 



*FlG. 4. Gum-bud disease of carnations. Cross-section of a Scott carnation, showing bacteria lying between 

 outer petals of unopened bud. The petals are stuck together (grown together in many cases) and unable to open. 

 Bacteria not in the tissues, and cause of disease unknown. Syringe-water contaminated by manure-water. March 

 1903. Glen Burnie, Md. 



Fig. 4.* 



