Cactus Spine: From Collecting to Guarding
BBC Earth｜Desert Worlds·The Green Planet

No matter how old a desert plant is, water is always precious, whether gathered from melting snow or a shower of rain. So, cacti have developed extraordinary adaptations that enable them to not only collect water but to retain it.
不管一株沙漠植物有多老，水总是宝贵的，不管是从融雪中还是从阵雨中收集。因此，仙人掌已经发展出非凡的适应能力，使它们不仅能够收集水分，还能保存水分。

Instead of leaves, which would lose precious moisture through evaporation, they have spines. Each spine has a tiny pad at its base where the water is absorbed and then stored in the great swollen trunk. A large saguaro can hold 5,000 litres of water and is able to do so because it has another special adaptation.
它们不长叶片，以免宝贵的水分通过蒸发而流失，取而代之的是刺。每根刺的基部都有一个小垫，水分在这里被吸收，然后储存在膨胀的茎干中。一棵大型的树形仙人掌可以容纳5000升的水，之所以能够做到这一点，得益于它的另一个特殊的适应能力。

The ridges on its surface are like the pleats on an accordion. They allow the saguaro to change its shape. After rain has fallen, the pleats expand and the saguaro fills up its water tank. In the dry times, it uses its water to grow, produce flowers and, eventually, seeds. Fully-loaded with thousands of litres of water, this saguaro won't need to drink a single drop for another year.
它表面隆起的纹路就像手风琴上的褶皱。它们能让树形仙人掌改变形状。下过雨后，这些褶皱就会扩张，树形仙人掌就会把它的“水箱”填满。在干旱的时候，它利用这些水来生长、开花，最终结出种子。满载着数千升的水，这棵树形仙人掌一年都不需要吸收一滴水。

But such valuable stores of water attract thieves. Now the spine's function changes from collecting to guarding. The spines of some species are a quarter of a metre long. Others are needle-like barbs that grow in clusters and easily break off in the skin of any animal that touches them. But perhaps the most vicious cacti belong to a group called the chollas.
但如此珍贵的水储备会招来盗贼。现在刺的功能从收集变成了保卫。有些种类的刺有四分之一米长。还有一些是成簇生长的点针状倒刺，极易在任何接触到它们的动物的皮肤上折断。但也许最造成伤害的的仙人掌属于一种叫做多刺仙人掌的种群。

This is called a teddy-bear cholla because of the thick coating of spines on it. But don't be deceived by the name, there is nothing cuddly about THIS particular teddy bear. In fact, it's the most dangerous plant in the desert, and I wouldn't dream of putting my hand anywhere near it without proper protection.
这种被称为泰迪熊仙人掌，因为它身上覆盖着厚厚的刺。但不要被它的名字骗了，这只泰迪熊一点也不柔软可爱。事实上，它是沙漠中最危险的植物，如果没有适当的保护措施，我做梦都不敢把手靠近它。

Look closely at the spine and you can see very clearly why they're so dangerous. Each is like a splinter of glass, sharp enough to pierce flesh and they're covered with backward-pointing barbs. Most animals know to keep clear.
仔细观察这些刺，你可以非常清楚地看到它们为何如此危险。每根刺都像玻璃碎片，锋利得足以刺穿皮肉，并且还布满了向后指的倒刺。大多数动物都知道要远离它们。

词汇表
melting snow 融雪
a shower of rain 一场阵雨
cacti ['kæktaɪ] 仙人掌（cactus [ˈkæktəs]的复数）
adaptation [ˌædæpˈteɪʃ(ə)n] 适应力，适应性变化；改编
retain [rɪ'teɪn] 保留，保持，保存
moisture [ˈmɔɪstʃə(r)] 水分，水汽，湿气
evaporation [ɪˌvæpə'reɪʃ(ə)n] 蒸发；消失
spine [spaɪn]（植物的）刺；脊柱，脊椎
pad  [pæd] 垫子，垫状物
saguaro [sə'gwɑ:rəʊ] 树形仙人掌，巨型仙人掌
ridge[rɪdʒ] 脊，隆起部分；屋脊；山脊
pleat  [plɪːt] 褶, 褶状物
accordion [əˈkɔː(r)diən] 手风琴；可折叠的
water tank [tæŋk] 水箱，水槽
fully-loaded 全负荷，满载
guard [ɡɑː(r)d] 保护，守卫，保卫
needle-like barb [bɑː(r)b] 针状倒钩
in clusters [ˈklʌstə(r)] 成群，成簇
break off 中断，折断，中止
vicious ['vɪʃəs] 凶险的，会造成伤害的
cholla ['tʃɔɪə] 多刺仙人掌
teddy-bear ['tedi beə(r)] 泰迪熊
coating 覆盖层，厚厚一层
cuddl: [ˈkʌd(ə)li] 令人想拥抱的，柔软可爱的
splinter [ˈsplɪntə(r)] （木头、金属、玻璃等的）尖碎片
pierce flesh [pɪə(r)s] 刺穿肉体
backward-pointing 向后指的，朝后的
keep clear 保持距离，远离；让路

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