412 PLANTS, SEEDS, AND CURRENTS 



as Christ offered some years after in his contribution to Engler's 

 Botanische Jahrbucher (1885). According to Christ, the oldest 

 constituents of the Macaronesian floras, such as occur in the Canaries 

 and to a less degree in Madeira, are the African plants, as examples 

 of which the Cactoid Euphorbias and the Dragon-trees (Draccena 

 draco) are amongst the first to attract the stranger's eye, when he 

 first visits these islands. Then followed the invasion by Asiatic 

 plants, now typefied by genera like Phoebe and Visnea, that are 

 identical with or closely allied to genera now existing in the warm 

 regions of Asia. Most of the peculiar Canarian genera appear to 

 be connected with these early African and Asiatic invasions. 



Since the American elements of the Canarian and Madeiran floras 

 seem as a rule to retain their original generic characters, we may 

 give third place to the invasion of American plants. They include 

 Clethra arborea, a beautiful ericaceous tree, the labiate shrubs of 

 Cedronella and Bystropogon, and species of the umbelliferous genus 

 Bowlesia, genera that in the aggregate are now most typical of the 

 warmer latitudes of South America and of the Andine region. The 

 special difficulties concerned with the origin of these American 

 elements of the Canarian and Madeiran floras are recognised by both 

 Hooker and Christ, and both of them find an explanation in the 

 transatlantic carriage of the seeds of the parent plants. Hooker 

 writes that " we can but hazard the assumption that at some very 

 distant date these genera existed in more eastern parts of South 

 America, from whence seeds were transported across the ocean " 

 (Marocco, p. 420). Christ appeals at once to the agency of the Gulf 

 Stream. However, no evidence of the fitness of these plant genera 

 for distribution by currents is produced, and I may say here, having 

 had a long experience of the buoyant capacities of seeds and fruits, 

 that the future experimenter will most probably find that the agency 

 of the currents cannot be invoked. It is possible that the problem 

 may assume quite another complexion, seeing that two of the genera 

 concerned, Clethra and Cedronella, exist in Eastern Asia, as in Malaya 

 and Japan. It may be that the American elements of the Macaronesian 

 floras may require the same general explanation that is apparently 

 demanded by the almost cosmopolitan connections that linked the 

 Canaries and Madeira in the earlier stages of their floral history 

 with the warmer regions of the globe. I refer to the original diffusion 

 of the same plant-types around the tropics. 



However this may be, the Azores were but little affected by the 

 early invasions of Macaronesia by Asiatic, African, and American 

 genera. Their floral history begins with the subsequent invasion 

 of the same region by South European and Mediterranean genera, 

 that now give character to the Laurel woods of the three Macaronesian 

 groups. But even this invasion must have taken place at a period 

 remote from the present. Although there has been no generic 

 dissociation, several of the trees and shrubs are not to be found 

 outside Macaronesia, and we should often look in vain in their 

 original European home for the parent stocks. Yet, as is shown 

 by Hooker and Christ, " the same plants, or their congeners or 

 close allies, are found abundantly fossil in the Tertiary strata of 



