GOOD: PMNr GEOGRAPHY 757 



found problems of fundamental importance. In short, he did much to restore 

 to it the prestige which, during the previous generation, it had seemed to lose; 

 and it is important to realize this because it helps to relate his work to that which 

 we must now go on to notice. 



Wegener's theory of continental displacement, or "drift" as it is sometimes 

 called, dates from about 1915, though it did not become common currency until 

 after the war, and its basic conception was not altogether novel. The relation 

 between ideas of continental displacement and plant geography is a double 

 one. First, the facts of discontinuity or disjunction, using those terms in their 

 widest sense, clearly provide some circumstantial evidence for or against the 

 view that displacement may have occurred; second, the idea is valuable to those 

 who would explain the fioristic relationships which today exist between the sepa- 

 rate continental masses. Both aspects combine to make drift a particularly live 

 problem for plant geographers. 



Up to the present, and despite an enormous amount of study from various 

 points of view, ideas of continental movement remain hypothetical. No summing 

 up of the matter is really possible, but the situation in relation to the geography 

 of the flowering plants, as it stands today, can be stated quite shortly. For at 

 least one hundred years — which means in effect ever since the subject of plant 

 geography took real form — there has been a common belief that the leading facts 

 cannot be explained at all satisfactorily so long as it is held that the geography 

 of the world, and particularly the isolation of the continents, has always been 

 as it is now. In this connection it is well to remember that there are two ways 

 in which a junction may be effected between separated entities. One is by inter- 

 posing something in such manner as to bridge the gap between them; the other 

 is by moving one or other of them bodily until the two come into contact. The 

 first method, since it did no violence to generally accepted beliefs, was for long the 

 accepted explanation; but it has aspects which, purely from the point of view of 

 the plant geographer, make it a less attractive proposition than the second. As for 

 the more direct geological and other evidences for displacement, these are at 

 present generally held to be inadequate, and those who favor this theory are 

 therefore faced with the fact that, on this ground, it is not generally acceptable 

 to geologists and geodesists. How far this essentially negative attitude of objec- 

 tion is justified time alone will show; but there are not a few who feel that the 

 rejection of a hypothesis simply on the ground of inexplicability is unwise. 

 Finally, with regard to Wegener's theory it must not be forgotten that it in- 

 volved not only continental displacement, but also the idea of a more or less 

 continuous movement of the poles. Any such movement would of course in turn 

 involve corresponding movements in the climatic zones of the world, and a pos- 

 sibility of this kind as an explanation of many difficult phytogeographical facts 

 has scarcely been sufficiently examined as yet. 



Early in the interwar years there came two important developments which 

 derived directly from the earlier work on glaciation already mentioned. The 

 more important was the growth, under the leadership of Erdtman (1943) and 

 others, of the technique of pollen analysis. This technique made it possible to 

 form various postulates from the proportionate occurrence of different kinds of 

 pollen grains in peat and similar deposits about the nature of the vegetation 

 contemporary with the deposits and thus to draw a much more complete picture 



