DISEASES OF PLANTS. 34.7 
are harmless, and, as yet, we know no means to 
prevent them. 
Tuber lignosum is met eh on trunks of trees. It 
seems to be produced partly by insects, partly by 
changes of weather. It arises from a disturbance in 
the active vessels of the inner bark, which by the 
application of stimuli, become several times con- 
voluted without forming buds or boughs. They 
form instead of this, great knobs, which often, in 
a bad situation, especially through moisture, exul- 
cerate. They not untrequently grow very large, 
without the least injury to the tree. 
§ Shy. 
Squamationes, or spongy swellings, are produced 
like galls. A small insect lays its eggs in the apex 
of a bud. ‘Thus injured, the branch, which was to 
evolve itself from the bud, cannot be properly un- 
folded, it remains quite short ; all its leaves, there- 
fore, expand themselves from one point, but they 
are of small size. The whole has somewhat the 
appearance of a rose. ‘Lhis may be often seen, 
particularly in willows. | 
Such sponeyswellings are of bad consequence ve 
in great numbers. ‘he only way to extirpate them, 
is, to cut them off, before they are properly formed. 
§ 318. 
The Bedeguar occurs in roses only, and has the 
same origin as the former, with this difference, that 
the insect which gives rise to the Bedeguar, deposits 
a number of eggs in one heap in the middle of the 
| 3 | bud. 
