1899] ON MIMETIC RESEMBLANCES 125 



rachis, resembling those of a rush, is characteristic of many marsh 

 plants, but is not confined to the genus Jiincus. Thus Oenanthc fistulosa 

 and Crantzia lineata (Umbelliferae), several Cassias, Spar Hum junceum, 

 etc. (Leguminosae), Scorzonera, Enhydra (Compositae), Convolvulus chon- 

 drilloides (Convolvulaceae), Johnsonia and Soivcrbia (Liliaceae), Bobartla 

 and Lansbergia (Irideae), are all good illustrations enforcing the same 

 conclusion as to the common origin of their common resemblances. 



Xerophilous Types. — One of the commonest mimetic features of 

 plants growing in very arid districts is to be spiny. Our own Genista 

 anglica (Needle-Furze) and ITlex europaeus (the Common Furze) will 

 illustrate it ; but " thorns and thistles " have been recognised as typical 

 of deserts from the earliest ages. 



That drought is the actual cause of spinescence in all cases has 

 been easily proved by growing such plants in a moist soil and air, 

 when the spinescence rapidly disappears. 



Another xerophilous and more remarkable type is the fleshy stem. 

 Thus the Cactaceae of Mexico mimic very closely the Euphorbias 

 with thick leafless stems of the Soudan, as well as the Stapelias 

 (Asclepiadaceae) of South Africa. As the conditions of life in which 

 these three groups live are the same, their peculiar vegetative structures 

 have been similarly evolved. 



Alpine Types. — One of the most characteristic types of vegetation 

 is that of the Cypress, Thuia, and Juniper, the leaves of which are 

 extremely minute and closely adpressed and imbricated along the 

 slender shoots. 



Now, we find this type of foliage exactly paralleled in, or mimicked 

 by Alpine species of the genus Veronica, which abound in' New 

 Zealand. The species of the lowlands are shrubby, with large leaves ; 

 those of a higher elevation begin (say) with V. buxifolia, so called 

 because its leaves resemble those of the box ; then on ascending to 

 4000 and 5500 feet there occurs V cuprcssoides, the specific name 

 indicating its mimetic resemblance to the Cypress; while at 8000 feet 

 V. lycopodioides is found, resembling the Lycopodium, or Club-Moss. 



As drought appears to be one of the direct causes of this diminished 

 type of foliage, it is not surprising to find it mimicked in the African 

 deserts by Salsola pachoi, etc. So, too, in the Antarctic regions, it is 

 exactly paralleled by that of Drapetes muscosa (Thymelaceae), Bolax 

 glebaria (Umbelliferae), Lyallia herguellensis (Caryophylleae), Forstera 

 glavigera (Stylideae). 



Muscoidal Type. — This is one of the extreme forms of high Alpine 

 as well as of Arctic and Antarctic forms. Besides the above-named 

 species of Veronica, there are Saxifraga bryoides, S. muscoides, Cherleria 

 sedoides, Silenc acaulis, etc. Lastly, Bolax glebaria (Umbelliferae), of 

 the Falkland Islands, is mimicked by species of Acantlwphyllum 

 (Caryophylleae), in Afghanistan, and by Haastia (Compositae), in New 

 Zealand. 



9 NAT. .SO. VOL. XIV. NO. 84. 



