4o6 



SCIENCE. 



[N. S. Vol. XVII. No. 429. 



the long tap-root and a few strong lateral 

 roots very near the surface of the soil. 

 In wet situations the tap-root soon disap- 

 pears, and the plant becomes surface-rooted 

 from the development of the lateral roots. 

 In a dry situation the tap-r.oot persists and 

 the initial lateral roots disappear. Trees 

 exhibiting this plasticity readily adapt 

 themselves to a great diversity of situa- 

 tions as to soil and moisture. Thus we 

 find the red maple grows in swamps, and 

 also on dry rocky ridges. 



It was further shown that the form and 

 behavior of the initial root system, in its 

 development prior to its becoming mate- 

 rially modified under the influence of en- 

 vironment, is directly correlated with the 

 soil moisture conditions best suited to its 

 gi'owth and development. It appeare pos- 

 sible to classify our woody plants into 

 groups based upon differences in form and 

 development of their initial root systems, 

 and their plasticity under the influence of 

 environment, and judge, with a fair de- 

 gree of accuracy, the locality as to soil 

 moisture best suited to each group. 



Observations on a Hitherto Unreported 

 Bacterial Disease, the Cause of which 

 enters the Plant through Ordinary 

 Stomata: Dr. Brwin F. Smith, Depart- 

 ment of Agriculture. 

 A disease of Japanese plums of unusual 

 interest has made its appearance in central 

 Michigan. It is first visible in the form of 

 numerous small water-soaked spots on the 

 leaves and green fruits. The leaf disease 

 ends in 'shot-holes'; the fruit -disease ends 

 in roundish, sunken, shallow black spots 

 and in deep fissures which spoil the plums. 

 The spots enlarge slowly, but may finally 

 reach a diameter of one fourth to one half 

 inch. The disease is due to a yellow bac- 

 terium, Pseudomonas pruni Smith, which 

 enters the imin^ured plant through ordi- 

 nary stomata. In the earliest stage of the 



disease, visible only under the compound 

 microscope in properly fixed and sectioned 

 material, the bacteria are confined to the 

 substomatic chamber. From this point 

 they push into the deeper tissues, and by 

 the time the spots have become large 

 enough to be seen under a hand lens (as 

 small water-soaked areas— one fifth to one 

 half mm. in diameter), the bacteria have 

 multiplied enormously in the depths, push- 

 ing up the epidermis and the cells imme- 

 diately under it, and forming in the deeper 

 tissues closed cavities of considerable size. 

 Later, when the enlarged spots have begun 

 to sink in and become brown, the bacteria 

 reach the surface as numerous tiny, 

 rounded, pale-yellow, gum-like masses, 

 which ooze from the stomata lying over 

 the closed bacterial cavity. The infec- 

 tions take place principally in May and 

 June and no wounds are necessary. The 

 shaded and west side of the fruits are 

 most subject to infection, i. e., those on 

 which the rain drops or dew drops (neces- 

 sary for infection) would persist longest 

 becaixse best protected from the morning 

 sun. This is primarily a disease of the 

 parenchyma, but the bundles are finally 

 invaded. 



The organism is distinctly yellow and 

 grows readily in ordinary culture media, 

 bouillon, milk, potato, agar, etc. It was 

 easily obtained in pure culture from small 

 spots. In agar plate cultures it looks much 

 like P. campestris, but is readily distin- 

 guished by its feebler growth on potato 

 and by its behavior in Uschinsky's solu- 

 tion, which is converted by it from a 

 limpid fluid to one as viscid as egg al- 

 bumen. The bacteria are small to medium 

 size and occur singly, in pairs, or short 

 chains. They are motile by means of one 

 to several polar flagellse. The thermal 

 death point is approximately 51° C. Gela- 

 tin is not liquefied rapidly. Litmus in 

 milk is reduced, but finally returns to its 



