How do plants make food? You probably think the answer is photosynthesis. This is the process by which plants take sunlight, water and carbon dioxide, and turn them into sugars and oxygen. You probably also know plants need chlorophyll, contained in green leaves, to do this. However, some plants cannot make food this way, even if they have green leaves. Instead, they attach themselves to other plants and steal their food. These are known as parasitic plants.

Plants that cannot photosynthesize at all are called total parasites. One example is the dodder, which has no leaves. It looks almost like a piece of string. To feed, it twists around a host plant and sucks the nutrients out of it. Unlike the dodder, dwarf mistletoe is a green parasite. It can photosynthesize, but it steals the water it needs from tree branches. A third kind is the flowering parasite, such as the famous rafflesia which measures a meter across. You will know if you walk past a rafflesia flower because it smells like a dead body! The chart on the next page contains more information on some common parasitic plants.

Parasitic plants in numbers
6 Thurber's stemsucker, which is found in North American deserts, is just six millimeters long.
10 The Australian Christmas tree, which local people call moodjar, can grow up to 10 meters high.
11 The rafflesia flower, which grows in Malaysia and Indonesia, weighs up to 11 kilograms.
90 Dwarf mistletoe shoots out its seeds – which are covered in a kind of glue – at up to 90 kilometers per hour.
201 There are 201 species of dodder, some of which produce white, pea-sized fruits in the summer and fall.

And not only plants are parasitic. There are also parasitic animals, fungi (mushrooms), bacteria, and viruses. They can spread through the air, through unclean food and water, and for humans, when we go to the toilet – which is why handwashing is so important!

植物如何製造食物？你大概會覺得答案是光合作用。這是植物將陽光、水和二氧化碳，轉化 為糖類與氧氣的過程。你大概也知道，植物需要綠葉裡含有的葉綠素，才能進行光合作用。然而，某些植物即使擁有綠葉，也無法以此方式製造食物。他們反而是附著在其他植物身上竊取食物。這就是所謂的寄生植物。

完全無法進行光合作用的植物，稱為全寄生植物。其中一個例子就是沒有葉片的菟絲子，幾乎狀似一條繩子。為了進食，它會纏繞在宿主植物上，吸收宿主的養分。與菟絲子不同，矮槲寄生則是綠色寄生植物。它會進行光合作用，但需要從樹枝竊取水分。第三種是會開花的寄生植物，例如直徑約一公尺的知名大王花。你如果經過大王花，一定會注意到它，因為它聞起來就像腐屍！右頁圖表則顯示某些常見寄生植物的更多資訊。

寄生植物的各類數據
6 Thurber's stemsucker 生長於北美洲的沙漠，只有6公厘長。
10 澳洲耶誕樹，當地人稱為「moodjar」，可生長至10公尺高。
11 大王花生長於馬來西亞和印尼，重達11公斤。
90 矮槲寄生能以高達每小時90公里的速度，噴發出包覆某種黏膠的種子。
201 菟絲子植物共有201種，有些會在夏季和秋季生產豌豆大小的白色果實。

而且不是只有植物有寄生特質。還有寄生動物、真菌（香菇）、細菌和病毒。它們能透過空氣、不潔的食物和水傳播，而在人類之間的傳播方式就是上廁所─這就是洗手之所以如此重要的原因！