94 



ESSENTIALS OF BOTANY 



each half of the leaf is plaited in a somewhat fan-like 

 manner, and the edges of the two halves are then brought 

 round so as to meet; in the lady's mantle the fan-like 

 plaiting is very distinct ; in the wood sorrel each leaflet 

 is folded smoothly, and then the three leaflets are packed 

 closely side by side. All these modes of vernation and 

 many others have received accurate descriptive names by 

 which they are known to botanists. 



111. Importance of Vernation. — The significance of ver- 

 nation is best understood by considering that there are 

 two important purposes to be served : the leaves must be 



Fig. 57. Development of an Oxalis Leaf. 



A, fnll-groTTO leal ; B, rudimentary leal, the leaflets not yet evident ; 

 C, more advanced stage, the leaflets appearing; D, a still more 

 advanced stage. (B, C, and D considerably magnified.) 



stowed as closely as possible in the bud, and upon begin- 

 ning to open they must be protected from too great heat 

 and dryness until they have reached a certain degree of 

 firmness. It may be inferred from Fig. 66 that it is 

 common for very young leaves to stand vertically. This 

 protects them considerably from the scorching effect of the 

 sun at the hottest part of the day. Many young leaves, 

 as, for instance, those of the silver-leafed poplar, the pear, 

 the beech, and the mountain ash, are sheltered and pro- 

 tected from the attacks of small insects by a coating of 



