SOME STRANGE GREENHOUSE PLANTS 



various forms from globular to cylindrical, and 

 varying in size, according to the limits of the 

 particular species. Now, what benefits do the 

 cacti derive from this modification of their 

 structure ? 



In the first place they obviously run no risk ot 

 getting their leaves scorched by the hot rays of 

 the sun ; in the dry atmosphere, their thick fleshy 

 structures can retain moisture in a manner that no 

 plant bearing ordinary branches and leaves could 

 possibly do. This is the keynote to their suc- 

 cess ; these cacti have become storehouses of 

 water against the time of drought. In the rainy 

 season they fill up their tissues with moisture ; 

 then comes the long dry period, during which, 

 however, their water is not evaporated by the 

 burning sun, for their outer covering skin is so 

 thick and strong that it retains the moisture within 

 the plant tissues ; indeed, these cactiform plants 

 have been very aptly termed ^' vegetable camels," 

 from the fact that they provide themselves with 

 large quantities of water while it is obtainable, and 

 store it against the time of need, which in such 

 lands is bound to come. 



Being without leaves, the leaf function of feed- 

 ing on gaseous foods from the atmosphere has to 

 be carried on by the plant body as a whole, hence 

 we find that its solid stem or globular mass is 

 green ; the green colouring matter being essential 

 to the feeding process. Now, by this concentra- 

 tion of material and storage of moisture, these 

 plants expose themselves to considerable dangers 



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