THE AZORES 



419 



in the order of their size — Juncus, 0-33 mm.; Calluna vulgaris, 

 Menziesia polifolia, Sibthorpia europcea, all 0-5 mm. ; Thymus serpyllum 



0- 66 mm.; Anagallis tenella, 0-75 mm.; Lysimachia nemorum, 1-0- 



1- 3 mm. ; Luzula, 1-3 mm. ; Potentilla tormentilla, 1*8 mm. 



The seeds of Juncus were found by Darwin and others in dried 

 mud adhering to birds. (I do not find many references to Juncus 

 in my notes, but species such as bufonius, effusus, capitatus, etc., 

 are characteristic of the Azorean flora.) Probably the seeds of plants, 

 like Anagallis tenella, that grow in boggy ground would be transported 

 in the same way. But one could scarcely appeal to such an agency 

 in the case of plants of dry moors, such as Calluna vulgaris and Men- 

 ziesia polifolia. Yet many birds frequent such moors, even gulls 

 and curlews in certain seasons, and it is possible that the minute 

 seeds of Calluna might become entangled in their plumage, when, 

 as often happens, they make their nests of heather. 



Except with Luzula and Juncus, the seeds of but few of the Azorean 

 moor plants would, according to my observations, emit mucus 

 when placed in water, or become slimy when moistened, a property 

 that enables seeds to adhere firmly to plumage on drying. But the 

 quality is a variable one, even with the same species, as is indicated 

 by their behaviour in my later experiments in England on the seeds 

 of Luzula campestris, L. pilosa, and L. sylvatica, and of species of 

 Juncus, a subject also dealt with in my previous work on the Pacific 

 Islands (p. 567). It is highly probable that a bird brushing past 

 such plants in wet weather would carry off on its feathers a number 

 of the wet seeds of Luzula and J uncus, and that they would adhere 

 firmly to its plumage when dry. The cause of this tendency to 

 become slimy and sticky when wetted is described by Buchenau 

 in the cases of the seeds of Luzula and Juncus in his monograph on 

 the Juncacece (Pflanzenreich, 1906, pp. 25, 30). It is well exhibited, 

 he says, in the case of a species of Luzula peculiar to the Canary 

 Islands. At least five of the nine European species of Juncus 

 found in the Azores display this property in their seeds, and several 

 of the species most widely distributed over the world are known to 

 exhibit it. The aid thus given to dispersal in the case of plants 

 of many different genera was emphasised in my book on Plant 

 Dispersal (p. 567) ; but it had long before been recognised by Kerner 

 and others, and Buchenau also lays stress on the part which animals 

 would thus play in the distribution of species of Luzula and Juncus. 

 As they brush past the plants in wet autumn weather they would 

 carry away either on their fur or on their plumage the sticky seeds 

 from the open capsules. 



Yet we are in the case of these small-seeded plants often brought 

 into contact with problems that raise other questions than those of 

 modes of dispersal. Let us take the three plants with seeds half 

 a millimetre in size, Calluna vulgaris, Menziesia polifolia, and 

 Sibthorpia europ&a. Calluna has a solitary species which is mainly 

 European, though it has obtained a hold on the Atlantic side of North 

 America. Menziesia has half a dozen species found in Europe, 

 4sia, and North America, but although one at least is common to 

 he eastern and western hemispheres, M. polifolia is confined to 



