树瘤是愈伤组织，在树木受伤后，细胞无性繁殖形成的一种自我保护。 树瘤的成因有多种，一般可分为外力损伤型与细菌侵染型。外力损伤型顾名思义就是树木接受物理性损伤后，由于筛管的断裂造成局部营养过剩，而引发的无序性细胞分裂形成瘤状组织。外力损伤型有时也包括病虫害引起的损伤，如天牛的蛀食。而细菌侵染型由于细菌种类的多样性，我们一般将其统称为瘤细菌侵染。 树瘤并不全是有害的，如某些树瘤可加工成花瓶，烟斗等艺术品，深受人喜爱。 花梨木树瘤尤为珍贵，颜色暗红，纹路绚丽，质地细腻，密实油润。
有株生满了树瘤的大树长在和那堆石头相距几步的地方。
A large tree, covered with those excrescences which are the warts of vegetation, stood a few paces distant from the pile of stones.
他走到那棵树下面，用手摸那树干的皮，好象他要认出并数清那些树瘤的数目。
He went up to this tree and passed his hand over the bark of the trunk, as though seeking to recognize and count all the warts.
宾利轿车最为人称道的是其出色的手工艺和苛刻的选材，每辆轿车至少需用四百张优质牛皮，约合十五头牛，所需木材均选用上等胡桃木树瘤。
Bentley cars are highly claimed for its excellent selection of crafts and harsh. Each car would need at least 400 high-quality leather, or about 15 cows, and all from the finest walnut wood.
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