126 PHILOSOPHICAL NOTES ON 



All this, however, is hardly necessary to prove, for if, on 

 evolutionary principles, it is admitted that the first beginnings of 

 life must have occurred in water, where we now still find 

 descendants and modern representatives of those ancient begin- 

 nings, it will follow as a consequence that the air-leaf is a 

 descendant of the water-leaf — the cladophyl of ferns being the 

 connecting link. But let us go on. 



Asa Gray* says that cladophyl is a branch assuming the 

 form and function of foliage, such as in Ruscus, 3Iyrsiphylluniy 

 asparagus, &c. Phyllocladium is a branch assuming the function 

 of foliage, as in cactus, Xylophylla, and others. Phyllodiicm is a 

 petiole usurping the form and function of a leaf -blade, as in the 

 Acacias, Oxalis, Sarracenia, &c. 



It will be seen at a glance that all these mean the same thing. 

 I have already endeavoured to show that originally the stem, 

 petiole, and midrib were one and the same thing, as in Delesseria, 

 so that the petiole, being a branch, the phyllodium returns to its 

 original form, the cladophyl. 



lliiscus, Myrsiphyllum, and others first acquired the form we 

 call the leaf proper of phcenogams. This then became abortive, 

 and assumed the functionless form of tooth, or stipel, when the 

 axillary branch reverted to the form of the seaweed cladophyl. 



In the Acacias, however, where, according to Asa Gray, 

 phyllodia " form the adult foliage of over 270 out of less than 

 300 species," it is the leaf itself (or its petiole) that reverts to 

 the cladophyl form, from which it originated. Curiously enough, 

 it acquires the same position, with regard to the stem, that it has 

 in seaweeds, its blade being somewhat perpendicular, instead of 

 horizontal. 



A large portion of the animal forms of Australia have continued 

 up to the present day their low type of marsupial origin. So, it 

 appears, have large numbers of vegetable forms continued the 

 forms of seaweed cladophyls, from which they originated. 



The phaenogamous plant, called Pkyllanthus Chantrieri 

 (Xylophylla) consists of leaf-like expansions of the stem. They 

 are pinnate branches, or cladophyls, as they are called in botanical 

 books. They are furnished with serrations or teeth on their 

 margins, like those of leaves proper. In the angles between the 



* " Struct. Bot.," p. 65. 



