INFECTION THROUGH STOMATA. 



63 



Recently, in the writer's laboratory, a bacterial leaf-spot of the cauliflower has been 

 studied by Lucia McCulloch, and has been reproduced very readily by spraying upon 

 healthy plants pure cultures of Bacterium maculicolum suspended in water, and here also 

 infections were through the stomata as shown by serial sections. 



In 1 90 1, Zimmerman described a tubercular or knot disease of the leaves of certain 

 Rubiaceous plants in Java, and figured a bacterial focus in the center of each little tubercle. 

 In the earliest stage of the disease, before any tubercle had developed, he found very small 

 nests of bacteria under certain stomata. It does not appear that he cultivated out any 

 of these organisms or reproduced the disease by inoculations, but his figures are good and 

 it is not likely that he was mistaken in the interpretation of his facts, or that the objects 

 figured as bacteria should be anything but bacteria. Further work needs, however, to be 

 done upon this disease. 



Pierce's bacterial disease of walnuts and the olive-tubercle are two additional diseases 

 which should be studied with reference to the possibility of infection taking place through the 

 ordinary stomata. I believe it may, especially in the former. In fact it is difficult to explain 

 the numerous spots on leaves, stems, 

 and green fruits, on any other hy- 

 pothesis. Pierce has reached the 

 same conclusion ; at least he has said 

 that infection takes place readily in 

 the absence of wounds. One spray- 

 ing experiment made by the writer 

 on a young olive shoot resulted nega- 

 tively, but more should be made to 

 permit of positive statements either 

 way. 



Several other cases are known 

 to the writer where bacteria enter 

 the plant and disorganize it through 

 the water-pores or through the ordi- 

 nary stomata, but enough has been 

 said to call general attention to the 

 fact, which is all that it was desired 

 to do in this place. 



Here, then, are a dozen well- 

 established bacterial diseases, the organisms causing which are able to enter and attack the 

 plants by way of the substomatic chamber in the absence of wounds and with only such 

 moisture conditions as occur very frequently in nature. There are probably many other 

 cases of this sort, and now that general attention has been called to the subject stomatal 

 infections will probably be found to occur right and left, although it was maintained by 

 Dr. Fischer, in 1897 and 1899, that not only has such a method of infection never been 

 made out, but from the very nature of the case never could take place (see page 15). 



Lenticellate infection. — When the epidermis of a plant gives place to a denser protective 

 layer (the cork) stomata disappear, and more or less imperfectly closed openings, known as 

 lenticels or cortical pores, take their place as aerating organs and are very conspicuous in 

 some plants. During some portions of the year, in certain plants, the lenticels form open 



*FiG. 16. — Stomatal infection of a broomcom leaf. Substomatic chamber full, but bacteria not yet occupying 

 intercellular spaces to any great extent nor any of the cells. Upper part of the bundle somewhat abnormal, possibly 

 a branch arising. Slide 412 An, left-hand section, fourth row. Drawn with a Zeiss 8 mm. apochromatic objective, 

 No. 12 compensating ocular and Abbe camera. Paraffin section stained with carbol fuchsin. For later stage see fig. 17. 



Note: The organism here in question may be known as Bad. andropogoni n. sp. It is non-sporiferous, polar- 

 flagellate (1-3), and white on culture media, forming small circular colonies on agar-poured plates. It is aerobic, 

 non-liquefying, non-reducing (nitrates) . For later stages of the disease see vol. i, plate 20. 



Fig. 16.' 



