39° BOTANICAL GAZETTE [MAY 
the great series. Sir JOSEPH examined the arctic flora from similar 
points of view. He explained the circumpolar uniformity which 
it shows, and the prevalence of Scandinavian types, together with 
the peculiarly limited nature of the flora of the southward penin- 
sular of Greenland. He extended his inquiries to oceanic islands. 
He pointed out that the conditions which dictated circumpolar 
distribution are absent from them, but that other conditions 
exist in them which account for the strange features which their 
vegetation shows. He extended the application of such methods 
to the Himalaya and to Central Asia. He joined with Asa GRAY 
in like inquiries in North America.- The latter had already given 
a scientific explanation of the surprising fact that the plants of the 
eastern states resemble more nearly those of China than do those 
of the Pacific slope. In resolving these and other problems, it was 
not only the vegetation itself that was studied. The changes of 
_ climate in geological time, and of the earth’s crust as demonstrated 
by geologists, formed part of the basis on which he worked. For 
it is facts such as these which have determined the migration of 
floras. And migration, as well as mutability of species, entered 
into most of his speculations. The essays of this magnificent series 
are like pictures painted with a full brush. The boldness and 
mastery which they show sprang from long discipline and wide 
experience. 
Finally, the chief results of the phytogeographical work of 
himself and of others were summed up in the great address on 
“Geographical distribution” at York. The Jubilee of the British 
Association was held there in 1881. It had been decided that 
each section should be presided over by a past President of the 
Association, and he had occupied that position at Norwich in 1868. 
Accordingly at York, Hooker was appointed President of the 
Geographical Section, and he chose as the subject of his address 
“The geographical distribution of organic beings.’ To him it 
illustrated “the interdependence of those sciences which the 
geographer should study.” It is not enough merely to observe 
the topography of organisms, but their hypsometrical distribution 
must also be noted. Further, the changes of area and of altitude 
in exposed land surfaces of which geology gives evidence, are 
