24 
Phaseoli EFS., forming like that bacterium, yellow colonies on agar. It 
is also monotrichic. : 
Life-history. This pathogene passes ‘the winter either in the debris 
of the host in the soil or on the seed. 
The Primary Cycle begins in the seedlings in the seed-bed or in the 
plants after they are set in the field. 
Pathogenesis. If the seed-plants have been diseased the seed 
may become contaminated with the pathogene when thrashed. On the 
oily coat of the seed, the bacteria may remain alive for a year or more. 
Examine the agar-plates on which contaminated cabbage seed have been 
sown. OBSERVE :— 
12. The yellaw colonies developing about some of the seed. 
DRAW. With your needle remove a bit from a colony to a small drop of 
water ona slide. Cover, examine and MAKE OUT:— 
13. The short rod-shaped bacteria swarming in the mount. 
Just how the pathogene on the seed gets into the seedling is not known, 
but it probably enters through the young rootlets. DRAW. 
The inoculum in the soil in the field is carried to the leaves of the grow- 
ing plants by snails, insects and probably by the wind. 
Examine the cabbage plant under the bell-jar. Here the conditions 
of humid weather are reproduced. OBSERVE :— 
14. The beady drops of water along the leaf-margins. This 
water is extruded from the water-pores at the ends of the veins. DRAW. 
In these drops the bacteria multiply and enter through the pore into the 
cavity at the end of the vascular bundle. Here they multiply rapidly, 
penetrate into the xylem-vessels and, traveling downward, kill and dis- 
organize the vascular tissues causing them to blacken. The pathogene 
thus reaches the stalk by way of the leaf-veins. 
Saprogenesis. It is not certainly known whether the organism 
multiplies in the dead and rotting leaf-tissues and in the soil; probably 
not to any great extent. It grows readily, however, in culture media 
as has been observed, forming characteristic yellow colonies. 
Secondary Cycles are initiated by bacteria carried by gnawing or 
sucking insects which have fed on diseased tissues. In this way the 
pathogene is carried from plant to plant and epiphytotics often result. 
Pathological Histology. Study the prepared cross-sections and oB- 
SERVE -— 
15. The deeply stained diseased vascular bundles. What 
tissues of the bundle are affected? 
16. The relation of the pathogene to the cells; inter- or intra- 
cellular? 
17. The numberless bacteria filling the spiral and annular 
vessels. Study the effects of the pathogene on the structure of these 
vessels as shown both in the cross- and longisections. 
Make prawincs to show these effects on the tissues. 
REPORT 
1. Describe fully the ways in which Bacterium campestre (Pam 
EFS. may possibly hibernate and show how these dete the em 
measures to be employed. 
