82 BACTERIA IN RELATION TO PLANT DISEASES. 



In the beginning of the rainy season, i. e., while the cane is still young, one often finds stem-tops 

 having an abnormal appearance (afwijkend uiterlijk) : The young leaves which have not wholly 

 unfolded show close to their bases lengthwise yellow spots, sometimes almost white spots, often com- 

 bined with a bruise (kneuzing) on the spot, with a few rows of small holes or with cracks. 



The top of the leaf is then usually green and sound. Sometimes only one leaf shows these abnor- 

 mal symptoms; sometimes a few leaves following each other show them all at the same time. 



If such sprouts are watched, it appears that the leaf attacked does not develop in the usual way, 

 but either breaks off across or cracks lengthwise, and acquires dark violet or black lengthwise stripes, 

 while the yellow spots become darker and soon show all sorts of colors. 



Usually the sprout keeps on growing without displaying much more externally. If, however, a 

 lengthwise section of the stalk is examined, it appears that this, at the point of the abnormal leaves, is 

 always somewhat thinner. If the disease occurs in severe measure, it may happen that the joint under 

 those leaves is faintly funnel-shaped, that is to say, at the top somewhat thicker than below, while the 

 joints between the same leaves show more or less clearly the same form, but at the same time are short 

 and remain as long as they are broad. Such places are later to be easily found again on the full-grown 

 stalks. 



As out of short joints roots sometimes develop, the entire part acquires naturally somewhat the 

 external appearance of a sereh-diseased stem, and the sign discussed here has been, without doubt, at 

 times taken for sereh. 



It is not impossible that both occur together. If, however, it is only Pokkah-bong, then the red 

 sereh stripes are wanting in the nodes. 



In all these cases it is possible for the top to grow on. One sees clearly then that the stem, where 

 the leaves are normal again, becomes also somewhat thicker and that the joints become longer. 



Notwithstanding this latter fact it is possible that the influence on the growing-point has worked 

 in such a way that the buds under the short joints sprout, although the terminal bud continues to 

 grow. 



This sign may in the Cheribon cane occur without previous Pokkah-bong, and occurs as a rule in 

 a few varieties which are not raised wholesale. 



When the cases of Pokkah-bong confine themselves to the above, the disease is of little conse- 

 quence. Only it must be observed that the affected stalks break off easily at the thin spots. 



Wakker made a microscopic examination of cases of top-rot and states that the young 

 leaves as well as the growing-point are changed to a soft-rot (brei) which consists of isolated 

 cells and bacteria, while the rest of the stem seemingly remains unchanged. The glassy 

 tissue shows the same structure as the normal stem; only the cell-walls are somewhat 

 thinner, and in cells and vessels everywhere bacteria are found. The peculiar glassy appear- 

 ance is caused by the air having escaped from the intercellular spaces to make room for the 

 watery bacteria-charged liquid which infiltrates everything. 



In the red rim are vessels and intercellular spaces filled with a more or less red-tinted 

 gum, which is in no wise different from that which is met with in other cane diseases, or in 

 connection with artificial wounds in the stem. 



In the vessels it is usually but lightly tinted; in thin section perfectly transparent, and 

 contains no bacteria. 



Outside the red rim there is usually nothing special to be seen. 



The difference in appearance (uiterlijk) between the top and the lower diseased stem 

 part is caused, no doubt, by the original difference of both these tissues. 



The top indeed consists of small cells with thin walls and much albumen; the older 

 joints, on the contrary, have much firmer walls that are less easily destroyed, and more 

 sugar. 



The inside of the cavities is usually lined with a thick layer of slime containing bacteria ; 

 the cells may here be more or less grown out and show a beginning of callous formation. 

 That is to say, it is possible that cells which border on the cavities are divided by cross-walls 

 which would otherwise certainly not have formed themselves. 



The circumstance that the gum in the vessels here contains at the outset no bacteria is 

 the main point of difference from Cobb's gum disease, since he states that the gum is full of 

 bacteria, and, in many cases, is said to be limited to the vessels. 



