New York AGRICULTURAL EXPERIMENT STATION. 183 
immersion in each of these in turn, followed by brief washing 
in alcohol, gave slides showing excellent differential staining. 
The organisms, the unaltered walls and the undissolved re- 
mains of the. middle lamellae retained the blue color and in 
the walls which had been fully acted upon the red color pre- 
dominated. Examinations of slides so stained have shown very 
interesting conditions. The Congo red also clearly reveals the 
solvent action, staining deeply the unaltered walls and giving 
but faint color to those from which the soluble part has been 
removed. The line of demarkation between such deep and 
faint staining tissue is very abrupt, indicating that the solvent 
action is rapid and complete after the penetration of the active 
substance. This action occurs some ten cells, more or less, in 
advance of the invasion of the organism. It is evident that 
the chemical agent causing this change penetrates the tissues 
and completes its action considerably in advance of the inva- 
sion of the organism. The rate of the invasion was clearly 
dependent upon the nature of the walls and the form of the 
cells. As already stated, no action occurs on cuticularized or 
lignified walls. Where the cells were much elongated in one 
direction the action progressed more rapidly in the direction of 
their longer axis. The organisms in the more recently invaded 
portions were chiefly found in the larger intercellular spaces 
at the angles of the cells. From these they made their way, 
evidently along the planes of the dissolved lamellae, occurring 
in the narrower portions as a Single line of rods lying end to 
ead. In no case were they within the cell cavities, although 
they often crowded the lumina of the open vessels. The walls 
themselves showed in these stained sections the same transi- 
tions noted in the fresh material, viz., swelling, and evident 
lamination of the inner lamellae preceding the full solution of 
the middle lamella. The middle lamellar substance itself, 
especially at the angles of the cells where it occurred in larger 
masses, showed distinctly a laminated or fibrillar structure 
when partially acted upon, indicating that it, like the wall, is 
not of entirely homogeneous structure. 
The discussion thus far has been based upon observations 
made upon carrot tissues. Studies of the invasion of turnip 
