136 PHILOSOPHICAL NOTES ON 



As the lower plants evolved into the higher, and organs of 

 i-eproduction became more differentiated and sj^ecialized, the leaves 

 became a subordinate part of the cladophyl or stem. In Sargassum 

 we see the branches not only already atrophied into teeth, but the 

 future leaf, the inflorescence, and the axillary bud of phaenogams 

 adumbrated. 



In the so-called entire margins of plants, these teeth may have 

 become altogether suppressed, if their ancestral leaves had them. 

 But there are also seaweeds without any teeth, or margin buds. 



These atrophied branches or serrations, like many other parts 

 of plants, have been a feature which, although apparently useless 

 in pha?nogams, could not be got rid of, but like the splint bones 

 of the horse, have been inherited through millions and millions of 

 generations. 



In Sargassum lacerifoUwn (Fig. 95) we further see where the 

 enlargement on the petiole of many water phrenogams, and at the 

 base of the leaves of certain cycads, &c., may have come from. 

 In seaweeds and water plants the bladdering of the petiole acts as 

 a float. 



Then this subsidiary idea of the derivation of ph^enogamic 

 leaf-teeth from cryptogamic cladophyl teeth would further support 

 the main idea, viz., that the leaf and the cladophyl are essentially 

 07ie thing. E. J. C. Esper (Icones Fucorum, 1800) shows Fticns 

 sanguineus,^ Tab. 38, as not only having a midrib but also veins 

 and suhveins. 



Looking at the whole question then from an evolutionary point 

 of view, I think the notion of the derivation of the phsenogamic 

 leaf from the seaweed cladophyl is not only highly probable but 

 irresistible. 



I think I have sufiiciently shown that, morphologically, there 

 is no essential distinction between the leaves of flowering plants 

 and the leaves of seaweeds. But in further support of this con- 

 clusion I should like to quote the opinion of a botanist, who has 

 been elaborating a similar idea. 



While in India, and before I had any facilities for reading what 

 others had thought and written on the subject of the leaf, and from 

 simple observation of the plants around me, I had come to tlie 



* 111 Esper's time every seaweed appears to have been called I^mcm^. The 

 thing is there pictured however, the name is of secondary importance, 



