A DESERT FRUIT. 67 



organisms entire from a single fragment, once diffused 

 equally over the whole body, is now confined to certain 

 specialized cells which, in their developed form, we know 

 as seeds or eggs. Yet, even among animals, at a low 

 stage of development, this original power of reproducing 

 the whole from a single part remains inherent in the 

 organism ; for you may chop up a fresh-water hydra into 

 a hundred little bits, and every bit will be capable o* 

 growing afresh into a complete hydra. 



Now, desert plants would naturally retain this primi- 

 tive tendency in a very high degree ; for they are specially 

 organized to resist drought being the survivors of 

 generations of drought-proof ancestors and, like the 

 camel, they have often to struggle on through long periods 

 of time without a drop of water. Exactly the same 

 thing happens at home to many of our pretty little 

 European stone-crops. I have a rockery near my house 

 overgrown with the little white sedum of our gardens. 

 The birds often peck off a tiny leaf or branch ; it drops 

 on the dry soil, and remains there for days without 

 giving a sign of life. But its thick epidermis effectually 

 saves it from withering ; and as soon as rain falls, wee 

 white rootlets sprout out from the under side of the frag- 

 ment as it lies, and it grows before long into a fresh 

 small sedum plant. Thus, what seem like destructive 

 agencies themselves, are turned in the end by mere 

 tenacity of life into a secondary means of propa- 

 gation. 



That is why the prickly pear is so common in all 

 countries where the climate suits it, and where it has once 

 managed to gain a foothold. The more you cut it down, 



F 2 



