March 14, 1902.] 



SCIENCE. 



406 



thorough knowledge of physiology, general 

 chemistry (preferably also organic chem- 

 istry), physics, general morphology of 

 higher plants, French and German ought to 

 be required. He outlined a course in 

 pathology beginning with the study of the 

 influence of enviromnental conditions on 

 the plant cell, followed by actual experi- 

 mental work with bacterial and fungous 

 diseases. Emphasis was laid upon the fact 

 that the plant should be considered first 

 and foremost, and that the student should 

 work with this himself. 



The Destruction of Cell Walls hy Bacteria: 

 Dr. Eewin F. Smith, Department of 

 Agriculture. 



Lantern slides were exhibited showing all 

 stages in the destruction of the inner tis- 

 sues of the turnip due to the parasitism of 

 Pseudomonas campestris. All were made 

 from one plant which was inoculated on 

 the blades of the leaves by means of needle 

 pricks, using a pure culture of this bac- 

 terium. The disease appeared on the leaves 

 only after a number of days. There was 

 a progressive downward movement of the 

 disease. The plant was removed from the 

 soil on the fifty-second day after inocula- 

 tion, at which time most of the leaves were 

 shriveled, but the root was white and en- 

 tirely sound externally. Sections of the 

 root showed the bacteria to be very abun- 

 dant in the inner parts. A careful micro- 

 scopic examination made at the time did 

 not reveal the presence of any fungi or ani- 

 mal parasites in the tissue. Cultures made 

 from the interior of this root yielded only 

 Pseudomonas campestris. Portions of the 

 root were fixed in strong alcohol and sub- 

 sequently infiltrated with paraffin, cut on 

 the microtome with a very sharp knife, and 

 fastened to slides with water containing 

 one-half per cent, gelatin, freshly prepared. 

 The paraffin was subsequently dissolved 

 out with turpentine, the sections stained in 



carbol-fuchsin, washed in water containing 

 50 per cent, alcohol, passed through graded 

 alcohols, dehydrated in absolute alcohol, 

 passed into xylol and finally mounted in 

 Canada balsam. A study of serial sections 

 with the best microscopic appliances has 

 failed to reveal the presence of any fungi 

 in the sections. The parts which are at- 

 tacked are only the inner pai'ts of the root 

 (vessels and parenchyma). Many of the 

 bundles are filled with the short bacterium, 

 and cavities in the parenchyma are found 

 around some of these bundles. The fixing 

 and subsequent treatment of the sections 

 allow the study of the organism in situ. 

 The bacterial masses are not torn or dis- 

 placed by the knife, and an examination of 

 these slides shows all stages in the solution 

 of the cell walls, from single cells or vessels 

 occupied bythe bacteria, to cavities occupy- 

 ing the place formerly occupied by hun- 

 dreds of cells and filled with the bacteria 

 and the remnants of the cell walls. The 

 cells are crowded apart by the growth of 

 the bacteria, and the middle lamella first 

 disappears, but the cell walls proper also 

 become vague in outline and finally disap- 

 pear. 



Oiservations on the Bacterial Rot of the 

 Galla Lily: Dr. C. 0. Townsend, De- 

 partment of Agriculture. 

 This is a soft broAvn rot, with offensive 

 odor, that usually attacks the bulbs but 

 may appear on the roots or leaves. It has 

 been observed to destroy the calla plants 

 in entire houses in the vicinity of Wash- 

 ington. As a rule, the bulb shows the 

 disease most frequently near the top, but 

 it often happens that the attack is made 

 below the surface of the ground, in which 

 case the bulb is commonly almost entirely 

 destroyed before the leaves indicate that 

 the plant is diseased. If proper conditions 

 prevail, the disease progresses rapidly and 

 the diseased tissue is broken doAvn. Agar 



