22 BACTERIA IN RELATION TO PLANT DISEASES. 



stains, unless they can be made to germinate. Many of the older identifications of 

 spores are untrustworthy. Alfred Fischer has shown that many of these determina- 

 tions rested on plasniolysis of the rods, i. e., on misinterpretations. Om^lianski 

 reports finding an oval spore which stains readily with ordinary' anilin stains. This 

 occurs in a rather large bacillus accompanying his hydrogen cellulose ferment. Dan- 

 napple reports finding spores which are very sensitive to heat ('99, Bibliog., XXXIII). 

 Usually only one endospore occurs in each cell, but Kern ('81, Bibliog., VIII), and 

 Schaudinn ('02, Bibliog., XI) have found bacteria with two in each cell. Excellent 

 directions for the study of spores are given in Part I of Migula's S^'stem der Bakterien 

 (see especially the second paragraph on p. 209). 



Cell-Unions— ZooGLCE^s:, Chains, Filaments. 



In some media bacteria are much inclined to separate after division ; in others 

 they remain attached in various wa\s. The most common method of union is an 

 irregular clumping, which in fluids gives rise to a fine or coarse flocculence. Such 

 unions also occur on solid media and may be designated zoogloege, or pscudo- 

 zooglcea-^ if one prefers to retain zoogloeae for the more intimately fused and com- 

 pacter gelatinous unions. Sometimes the organisms remain attached end to end. 

 Where the segmentation is distinct, such unions are designated chains. When 

 very long and with obscure segmentation, they may be called filaments. Is 

 there any true branching? What especial conditions of the culture medium favor 

 the formation of zoogloeae, of chains, and of filaments? Many bacteria form 

 zoogloese, chains, or ver}' long filaments under certain conditions, while under other 



Fig. 17.* 



conditions they remain as ver^' short, straight rods. (Compare figs. 18 and 19.) 

 As in case of involution forms unfavorable cultural conditions (thermal, nutrient, 

 etc.) appear to have much to do with their appearance. 



The growth of bacteria may be studied in hanging drops of bouillon, etc. Hol- 

 low-ground slides (fig. 20) should be used for this purpose, rather than ring-cells, 

 especially with high powers. Hill's hanging-block method is also serviceable 

 ('02, Bibliog , XVII). 



*F]C. 17. — Double blow-bulb for attachment to drop-bottle shown in fig. 16. By use of this de- 

 vice one oljtains with a minimum of pumping a constant small stream of water very suitable for 

 washing stained covers, etc. Made by Emil Greiner. It is best used with a larger flask than that 

 shown in fig. 16. Bulbs which have been long in stock should not be purchased, as the rubber de- 

 teriorates rapidly. 



