201 



obtains conditions nearest to those under which it grows on 

 the mainland. Locally it may almost be said to become 

 dominant, but it quickly disappears where the soil is more 

 compact. 



V egetatiori' of the Roof. — There are three main associa- 

 tions to be recognized on the roof of the island, but in the 

 limited time that was available to examine them it is difficult 

 to describe them in other than a static sense. Their possible 

 relation to each other as members of a succession will be 

 discussed shortly below. 



(i.) Rhagodia crassifolia, open shrubland. — This is the 

 most stable type of association seen upon the island. Low 

 bushes of Rhagodia crassifolia, 1 ft. to 2 ft. high, cover con- 

 siderable areas, this being almost the only species in the com- 

 munity (pi. xi., fig. 1). The association is an open one, with bare 

 patches between the bushes, but it is thought that biological 

 factors in the form of mutton birds and rats are largely respon- 

 sible for this, and that, if these were removed, the covering 

 of Rhagodia crassifolia would quickly be complete. The white 

 ground seen in the foreground (fig. 1) is caused by mutton 

 bird burrows, while in other places the Franklin Island rat 

 (Leporilhis jonesi, Thos.) had gnawed down portions of bushes 

 near to the ground and used the stems to construct its house 

 or wurlie, around other living bushes (see No. 2 of this 

 series.) 



The only other plant noted in this association was 

 Siloxeriis tomentosus, a small deep-rooting annual, the 

 numerous wiry stems of which grow at first prostrate, then 

 turn erect, and are terminated by characteristic compound 

 capitula of yellow flowers. 



The prevalent colour of the vegetation here in January 

 was a dull grey-green. 



(ii.j Frankenia fruticulosa association on travertine pave- 

 ments. — Pavements of travertine or nodular limestone occur 

 at all levels from a few feet above the shore line to high points 

 on the roof. They all bear a characteristic flora of which 

 Frankenia fruticulosa is the most typical species (pi. ix., fig. 

 1; pi. X., fig, 2). This is a mat-forming woody plant, which, 

 though it sometimes forms a small tap root, also develops 

 adventitious roots freely on the underside of its prostrate 

 stems. The stems, except in the oldest parts, are hidden by 

 numerous opposite linear-cylindric leaves (3 to 4 mm. long) 

 standing erect. The leaves are almost grey owing to hairs, 

 with only a tint of subdued green. Tliey are also revolute, 

 showing a pronounced groove on the under-surface. The thin 

 wiry roots run horizontally at no great depth in the sandy 

 soil between the limestone blocks. They have a solvent action 



