420 BOTAXICAL GAZETTE [may 



argument upon statistics. In accordance with his theory he made a number 

 of predictions as to the distribution of species in New Zealand. These pre- 

 dictions have been verified by statistics which he has collected there, and 

 which he presents in his latest paper, furnishing a very striking verification of 

 his theory. 11 



Supposing a given species to have entered the islands at a certain point, 

 and spread at an even rate, the area of its distribution at any time would be 

 a measure of its local age. It is reasonable to suppose that this species would 

 give rise to endemics, in increasing number as time went on, and as the area 

 occupied became greater. At the limits of the islands farthest from the point 

 where the species entered, the local age of the species, and consequently the 

 number of endemics to which it had given rise, would be least. Following out 

 such a conception, Willis predicted that the middle zones of the islands should 

 show a greater number of endemics than the outer zones, and this proved to 

 be the case. 



Following the same line of thought, those endemics which were produced 

 early would have most nearly reached the limits of the islands in their dis- 

 tribution, while those produced later in the local history of the parent species 

 would be more limited in their distribution to the middle zones of the islands. 

 Consequently, the author predicted that "the range of an endemic species 

 would on the average be greater the nearer that one of its limits w T as to either 

 end of the islands.' ' This also was verified. 



Another prediction made and verified was that widely distributed species 

 would be more widespread within the islands than endemics, as in the case of 

 Ceylon. On the basis that the land connection with New Zealand both ended 

 earlier and began earlier than that with Ceylon, the author predicted that the 

 average area occupied by a species in New Zealand would be greater than in 

 Ceylon, that is, that both "wides" and endemics would be comparatively 

 fewer in the lower or earlier stages in the scale. These predictions also were 

 verified. 



Those who wish to examine the exact mathematical statement of the 

 author's method and conclusions are referred to the paper. — Merle C. 

 Coulter. 



A floating reed swamp. — Occurring in the delta of the Danube River is 

 a remarkable form of floating swamp formed by the reed Phragmites communis 

 var. flavescais Gren. and Godr. It has been described by Miss Pallis, 12 who 

 visited and studied it in 191 2 and again in 1913. She found that this swamp, 

 known as Plav, differs from a closed reed sw r amp chiefly in the fact that it 

 floats, the surface of the mat of soil and vegetation remaining constantly about 



11 Willis, J. C, The distribution of species in New Zealand. Ann. Botany 30: 

 4-457. fig. I- 19 1 6. 



12 Pallis, Marietta, The structure and history of Plav, the floating fen of the 

 delta of the Danube. Jour. Linn. Soc. 43:233-290. pis, 11-23. 1916. 



