84 



FIRST STUDIES IN PLANT LIFE 



going on at its fastest that the lobed leaves are made. 

 Think of the strong rush of sap up the chief ribs, and 

 you will see that the leaf is likely to grow faster 

 towards the points c, d, and g, than at the points n, k, 

 m, 0. Later on, when the rush of sap is not so strong, 

 no part of the edge is pushed out more than another, 

 and so we have the shape shown in the upper leaf. 

 This, remember, is only a guess ; but there are many 

 other facts to support it. Examine the toothed and 

 the entire leaves of the honeysuckle, and look at the 

 strongest and weakest leaves of the morning glory 

 convolvulus and of the bramble. You see, then, that 

 there is still much to find out as to the cause for the 

 shapes of leaves, but the main fact is clear : the leaves 

 seek air and light, and it is this that fixes shape and 

 size and position. 



13. Leaves that catch flies. To the root-food and 

 the air-food, some plants, like the sundew, add food 



got by catching flies ; 

 and in these cases, the 

 form of the leaf is altered 

 for this purpose. The 

 leaves bear hairs with 

 sticky blobs of "dew' 

 that catch insects. At 

 the touch of a fly, the 

 sticky dew increases, and 

 the hairs curve over the 

 insect. When the leaf 

 has eaten all the soft 

 parts of the fly, the hard 

 parts are pushed off the 



Whittakers sundew (after von Mueller), leaf. Pull Up a SUlldew 



