74 



BACTERIA IN RELATION TO PLANT DISEASES 



upper ones shortened and bearing fan-shaped foliage. Most authors speak only of a red substance in 

 the vascular bundles, and it is generally designated as gum. 



The red granular substance in the vessels also stains red the walls of the ducts. This red pigment 

 is soluble in alcohol. The sieve-tubes are also plugged by it. This plugging of the vessels is said to 

 result in a checking of the growth, the fan-like arrangement of the leaves, and the sprouting of the 

 shoots and of roots from the stem-nodes. The degree of the plugging of the vessels is dependent upon 

 various conditions a rich water-supply and a rapid growth are unfavorable to it. The gum is chiefly 

 in the nodes (Valeton). Valeton also speaks of finding in the sieve-vessel portion of the bundle a few 

 cells holding nuclei, which spread themselves to a large extent and crowd out the surrounding sieve- 

 vessels and duct-cells. 



According to Soltwedel there is a degeneration of the cellulose into drops of a very refractive sub- 

 stance. This change is accompanied by the formation of the gummy substance, liquid at first, later 

 hardening and plugging the greater part of the vessels. Secondarily, the duct-cells become red; the 

 gum which is formed becomes red also. 



(12) A yellow gum or slime in the vascular bundles. Valeton, who appears to have studied the 

 anatomy of the diseased cane with greater care than any other student of Sereh, speaks frequently of 

 the gum being of various colors, first as nearly colorless or yellow and later on becoming red. I trans- 

 late the following paragraphs from his first paper : 



"This refractive gum may be perfectly colorless, or vary through all the tints of light yellow, 

 amber, brown to dark red, black and violet. * * * 



"In lengthwise cuts it appears that the red color of the gum is local, and confines itself to the node. 

 By a vertical cut through a vessel, one sees then in the node the gum colored dark red or yellow, and 

 both upward and downward becoming lighter, often very suddenly, and before long wholly colorless 

 and scarcely refractive. * * * 



"Generally it gives the impression of a thick syrupy mass of very unequal toughness and fluidity, 

 which during a slow movement through the vessels, gradually coagulates and becomes woody. * * * 



"Often there are in these net-works [of gum] quite equally distributed corpuscles, probably small 

 gum particles, which, while of about equal size in one and the same division of the vessel, differ greatly 

 in size in the different divisions from being scarcely visible to being noticeable with but a weak mag- 

 nifier. * * * 



"In the gum itself, which then, however, is never woody and which sometimes even in the cold by 

 a long continued influence dissolves in potash, similar extremely fine little dots often occur quite uni- 

 formly distributed. These, then, especially give the impression of bacteria distributed in the gum, but 

 it was not possible for me to observe a well-defined form. Others give the impression of micrococci. 

 * * * 



"Many of the bundles of the node-vessel-net also contain gold-yellow gum. * * * 

 In the germination of Sereh-diseased cuttings, Valeton says that occasionally "greatly swollen 

 eyes occur, the oldest middle vessels of which are filled with thick, yellow gum. " In this connection, 

 see figure by Cobb in his third report, of a section through a bud diseased by the Australian bacterial 

 disease. Cobb's figure corresponds exactly to Valeton's statement. 



(13) Signs in the parenchyma. Valeton mentions the very constant presence of oily or resinous 

 drops in the parenchyma; and of shining, colorless, yellowish or occasionally red drops which are 

 stained a faint violet to dark red in Hanstein's violet, and are insoluble in glycerin, boiling water, or 

 cold nitric acid. These latter are said to be distinctly peculiar to Sereh-diseased cane. He says that 

 they occur throughout the entire parenchymatic tissue of the lowest part of the cane and in the nodes ; 

 often also in the white sclerenchyma, which there surrounds the vascular bundles. 



Here and there in the parenchyma also appear parts in which the gumming has taken place. 

 The walls are then colored red or yellow, and the intercellular spaces filled up with thick gum drops 

 proceeding from the wall (which drops show the woody reaction), or with masses of granular sub- 

 stance. (Valeton.) 



Janse also speaks of the occurrence of yellow and brown spots in the interior of the parenchyma. 

 These spaces were full of a fine granular substance, which he says was not crystalline, and not bacte- 

 rial, from which, however, he claims to have cultivated out his Bacillus sacchari. 



All the signs do not appear together or in the same degree of severity. The extremes are desig- 

 nated as f 1 ) "banquet," "secondary, " or "transmissible" Sereh, in which all the signs are present; and 

 (2) as "primary" Sereh, in which there is only more or less reddening of the bundles, especially in 

 t In ise which are ci mnected with the leaf -sheaths at the nodes, the plant showing no external abnormal- 

 ities above ground, and only in some cases a few of the roots dead. Between these two extremes 

 there are all kinds of intergrading. 



