192 THE LEAF 



If the divisions of such a leaf are similarly compound or divided, 

 appropriate terms are formed, such as Bi-ternate (Fig. 552), Tri-ternate, 

 and so on. Similarly named sub-divisions of the pinnate form exist, 

 the bi-pinnate (Fig. 563), tri-pinnate (Fig. 556), and so on. 



These terms are also sometimes applied to the similar divisions of 

 pinnatifid lea^'es. Just as we have found that the number of pairs of 

 primary veins of the simple leaf is generally characteristic of the species, 

 so we find that the number of pairs of pinnae, technically known as 

 Jugae, is equally so. This number, therefore, should always be stated, 

 the leaf being designated as Bi-jugate, Tri-jugate, Multi-jugate and 

 so on. 



Two classes of pinnate leaves are recognized, in accordance with 

 their termination in a pair or in a single terminal leaflet. Those ending 

 in a pair (Fig. 554) are called Pari-pinnate, Even-pinnate, or Equally- 

 pinnate, the others (Fig. 555) Impari-pinnate, Odd-pinnate, or 

 Unequally-pinnate. 



When the divisions of a pinnate or a pinnatifid leaf are alternately 

 large and very small (Fig. 557), it is called Interruptedly-pinnate or 

 Pinnatifid. 



When the leaflets or divisions are turned backward so that they 

 point more or less in the direction of the base (Fig. 558), the leaf is 

 Runcinate. 



When the terminal division is very much larger, especially broader, 

 than the lateral, the leaf is Lyrate (Fig. 559) . 



Modified Leaves. — Coming now to consider the subject of character- 

 istic modifications in the form and function of the leaf, we note that 

 some of them pertain to the entire leaf, others to its individual parts. 

 We also note that in some of the modifications the entire leaf or one of 

 its parts retains the ordinary functions of absorption and assimilation, 

 the new function being added thereto either by partial change of the 

 entire leaf, or the complete modification of one or more of its parts, 

 while at other times the original functions are entirely lost. 



Carnivorous Leaves. — The function of absorbing and assimilating the 

 ordinary forms of nutriment is sometimes supplemented by that of 

 absorbing and assimilating animal tissue. In this case the leaf pro- 

 vides special forms of apparatus for enticing, intoxicating, or mechan- 

 ically catching, killing and digesting the animal, commonly an insect. 



The Pitcher Planf. — One of these forms is illustrated in the pitcher 

 plant (Fig. 560), in which one portion of the leaf becomes converted 

 into a vessel containing liquid of variable origin and complex compo- 



