THE BUD-ROT OF PALMS IN INDIA. 249 



The ends of the young germ-tubes from germinating spores 

 possess the power of boring through the wall of the sporangium. 

 Penetration is effected by the exudation of a solvent liquid, which 

 is almost certainly, from the analogy of other known cases, a cellu- 

 lose-dissolving enzyme, from the tip of the germ-tube. This was 

 clearly observed in cases in which zoospores germinated within the 

 sporangium, as in those figured in plate IV, fig. 15. Figs. 15a and h 

 show a spore which failed to escape through the mouth of the sporan- 

 gium, and after swarming for a time within it, came to rest and sur- 

 rounded itself with a wall as usual. A couple of hours later it had 

 germinated and the germ-tube had reached the opposite wall of the 

 sporangium. The apex of the germ-tube now swelled up and be- 

 came closely appressed to the wall. A vacuole occupied its tip. 

 Some time after, it was noticed that an area of the wall considerably 

 larger than that in contact with the tip of the germ-tube had under- 

 gone an alteration, which was visibl J in profile as a gelatinous swell- 

 ing in which the sharp double contour of the rest of the wall was lost 

 (fig. 15a), and from above (surface view) as a light, extremely trans- 

 parent spot (fig. 156). The swollen portion of the wall was clearer 

 than the rest. Actual penetration was not observed in this case, 

 but fig. 15c shows the ultimate condition from another similar case. 

 The same power of penetrating cell walls is possessed by the 

 haustoria, which are able to enter the parenchymatous tissue cells, 

 but are not found in those of the vascular bundles. The ordinary 

 vegetative hyphae are, however, unable to enter the host cells, but 

 grow exclusively between them ; in other words, their tips do not 

 excrete a cytase. 



When a leaf is first infected, the infection may arise from 

 germinating spores or from vegetative mycehum. The latter is what 

 occurs when a leaf-sheath is infected from another in contact with it, 

 as happens regularly during the progress of the disease towards the 

 centre of the crown. In this case it is probable that penetration 

 occurs through the stomata, which are numerous on the outer sur- 

 faces of the leaf-sheaths. In tracing the disease inwards through 



