86 BACTERIA IN RELATION TO PLANT DISEASES. 
with the tomato juice by adding 5 per cent of the dried precipitate directly to the juice. Here the 
retardation was nearly one-half. These vegetable juices were titrated and the acidity shown to be 
as follows: tomato, +5 per cent; carrot, +2 per cent; radish, +0.75 per cent. 
_ Effects of Other Bacterial’ Products—A small amount of some undetermined acid is produced 
by this organism in the presence of carbohydrates. In order to determine the effect on the enzym- 
action of this or other products of the bacterial metabolism, broths of various kinds in which the 
organism had been grown, were sterilized and their enzym content destroyed by heating to 80° C. 
To two parts of each of these heated broths was then added one part of a water solution of the 
precipitate containing the enzym, and a comparison was made of the activity of these mixtures 
and that of a solution of like strength of the precipitate in pure water. There was more or less 
inhibition in the broths in every case. The evidence, therefore, is that the products of bacterial 
metabolism inhibit rather than aid the cytolytic action of the organism. 
There is no diastasic action worthy of note, although a slight tendency to the extremely slow 
conversion of starch into amylodextrin has been observed. No erosion of the starch grains takes 
lace. 
: There have been many opinions regarding the composition and origin of the middle and inner- 
lamelle of cell-walls. Comparatively recently it has been shown that the ‘cellulose,’ of which it 
has long been known that parenchymatous walls are composed, includes a group of closely-related 
compounds. Moreover, the middle lamella does not give the cellulose reactions and the inner lamellz 
contain other substances in addition to cellulose. 
Cross and Bevan (1895), in their work on celluloses make two groups, (1) the cellulose group, 
(2) the compound celluloses. The cellulose group is further subdivided as follows: 
(a) Resistant to hydrolysis, e. g., cotton. 
(b) Less resistant to hydrolysis, found in grass stems, etc. 
(c) Low resistance to hydrolysis, found especially in fleshy roots and in seeds. 
Groups (a) and (b) are termed the celluloses proper, group (c) “ pseudo-cellulose’’ or ‘‘hemi- 
cellulose,” the name used by Schultz. By “‘hemicelluloses’’ are meant ‘substances closely resem- 
bling in appearance the true celluloses but easily resolved into simpler carbohydrates by the hydrolytic 
action of an enzym or of the dilute acids or alkalis.” 
The compound celluloses are divided into three groups:* (1) ‘‘ Pectocelluloses’’ of which the 
middle lamella is composed, (2) ‘‘lignocelluloses’’ which we commonly know as “wood,” (3) 
“‘cutocelluloses”’ constituting the protective outer layer ‘‘cutin.” 
Of the compound celluloses those termed “ pecto-celluloses’’ by Cross and Bevan, constitute 
the middle lamella and the other wall elements upon which the carrot rot enzym acts. It was 
Fremy (1840, 1848), who found in plant cell walls, along with cellulose, another substance which he 
called pectose, and he also isolated from certain plant tissues (carrot roots among them) an enzym 
capable of gelatinizing this pectose and related compounds. This enzym he called “pectase.’’ 
Fremy’s observations and conclusions have been confirmed by chemists, and the pectose series of 
compounds is classed with the celluloses as Cross and Bevan’s classification shows. Mangin’s most 
extensive studies (1888-1893) prove that here again we are dealing not with a simple compound but 
a complex of closely related compounds. ‘These he divides into two natural series, the one neutral, 
the other acid. Pectose belongs to the less soluble neutral series, and pectine is a more soluble form. 
Both of these are widely distributed, especially in the walls of young tissues. Pectic acid and its 
insoluble salt, calcium pectate, are of common occurrence and of peculiar interest to us. Fremy 
supposed that his enzym, pectase, clotted the pectose solution by converting the pectoseinto pectic 
acid, but Bertrand and Mallevre (1894, 1895) have proved that this clot is calcium pectate. Payen 
believed that the middle lamella is composed largely if not wholly of this salt and this belief has 
been confirmed by the recent studies of Mangin, and Bertrand and Mallevre, who have also shown 
that the inner lamelle contain varying proportions of pectose or pectic compounds in addition to 
the celluloses. 
Mangin’s studies led him to conclude that the wall, in the early stages of its development 
consists for the most part, of the less soluble pectose, whereas later the calcium pectate predominates 
in the middle lamella, and the pectose which is present is in the inner lamella, i. ¢., nearer the cyto- 
plasmic layers. The proportion of cellulose becomes increasingly greater, however, as one passes 
farther away from the middle lamella. The splitting of the walls along the middle plane under the 
action of pectate solvents indicates the probable occurrence of a thin sheet of calcium pectate even 
in the young walls. This layer thickens and becomes more clearly defined until it is plainly visible 
in the mature cell as the middle lamella. 
*Cross, article on Cellulose, Encyc. Britannica, 11th edition, 1910. 
