88 FIRST STUDIES IN PLANT LIFE 



6. Leaves that check the loss OT water. A thin, soft 

 leaf would be burned up at once in the desert ; 

 and so the cactus has a hard skin to keep the water 

 from escaping quickly from its thick leaves. Other 

 desert plants check the escape of water by having 

 their leaves tough and narrow or curled under 

 at the edge ; others, again, have salt in the sap, and 

 this, too, prevents the moisture from escaping quickly. 

 A thick coat of hairs is often used, especially on the 

 underside of the leaf, to check evaporation. It was 

 only the other day that it was found out that heat does 

 not easily pass through a spray of perfume ; but, for 

 ages, some of the plants of hot lands have been soften- 

 ing the effect of the sun's rays by throwing off perfume 

 from their leaves. This may give to you a new view 

 of the scents that come from the oil in the leaves of 

 our gum trees. 



7. How leaves are guarded against animals. 



Some leaves guard themselves against animals by keep- 

 ing flat on the ground ; others are passed over because 

 they have a taste that the animals do not like ; while 

 others again, like the gorse, lift themselves boldly up 

 and defy the animals to touch them. 



8. Plants that lie flat on the ground. How 

 cleverly the dandelion flattens itself out on the 

 ground ? Even when its time of flowering comes, and 

 it must hoist up its flower, it waits till it is quite ready 

 to open. Then up it goes, to get the help of the sun 

 and the wind and the bees. When the pollen has 

 done its work, down the flower falls again to be out of 

 danger while it is ripening the seed. As soon as it 

 is ready to open out into the beautiful seed-balloon, 

 the stalk rises again, lengthening itself so as to 



