CHAPTER III. THE LEAF. 



35 



time to indicate the arrangement of the segments or lobes, the 

 modifying adverbs pinnately and palmately, or radiately, may 

 be used, as pinnately quadrifid, palmately multisect, 

 radiately trilobate, etc. 



A leaf which is pinnately-parted in such a man- 

 ner that the divisions are linear and stand out from 

 the axis, parallel to each other, as the teeth of a 

 comb, is commonly described as pectinate, see Fig. 

 113. Leaves which are separated into numerous 

 Fig. 113. irregularly branching divisions are described as dis- 

 sected, and such leaves may be either palmately-dissected, as the 

 submerged leaves of the Yellow Water 

 Ranunculus, Fig. 114, or pinnately-dissected, 

 as the leaves of Chamomile, Fig. 115. 



It not infrequently happens that the 

 segments of a deeply indented leaf may 

 again be incised, lobed, etc. Such forms, 

 according to the depth of the incisions, 



Fig. 114. 



Fig. 115. 



and the arrangement of the segments, are 

 sected leaf of a the Veiiow described as bipinnatifid, bipinnatisect, bi- 



Water Ranunculus. , , . . 



f,g. it5 . Pinnately dis- Penalised, etc. 

 sected leaf of chamomile. Compound Leaves. A compound 



leaf is one whose blade is divided into two or more distinct sub- 

 divisions, called leaflets. These leaflets may possess stalks or 

 petiolules of their own, and in many cases they are fastened to 

 the main axis by means of a joint ; but frequently also the 

 leaflets are sessile, that is, attached directly to the main axis. 

 In case, however, the parenchyma of the leaflet is confluent with 

 the axis it is regarded as a divided simple leaf, and not as a 

 compound one. It will be seen, therefore, that the transition 

 from simple to compound leaves is a very gradual one. As a 

 matter of fact, in some instances it is difficult to say whether a 

 given form should be regarded as simple or as compound. 



Since the compounding or branching of a leaf always follows 

 the plan of venation, we may have either pinnately or radiately 

 compound leaves. 



The following are the most important of the pinnate forms : 

 The pari-pinnate, or abruptly pinnate, in which the leaf is 

 terminated abruptly by a pair of leaflets, as in Fig. 116 ; the im- 



