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 

 place. 



There have been many opinions regarding the composition and origin of the middle and inner- 

 lamellae 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 lamellae 

 contain other substances in addition to cellulose. 



Cross and Bevan (1895), in their work on celluloses make two groups, (i) the cellulose group, 

 (2) the compound celluloses. The cellulose group is further subdivided as follows: 



(a) Resistant to hydrolysis, e. g., cotton. 



(6) 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 in to simpler carbohydrates by the hydrolytic 

 action of an enzym or of the dilute acids or alkalis." 



The compound celluloses are divided into three groups:* (i) "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 pectose into 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 lamellae 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 lamellae, i. e., 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, nth edition, 1910. 



