GOOD: PLANT GEOGRAPHY 755 



deals with plant dispersal, will long remain a classic source of fact and commen- 

 tary on that subject and its many related problems. Eather later on, and partly 

 in association with Willis, Guppy turned his attention toward historical plant 

 geography, and two of his papers in this field. The Island and the Continent 

 (1919), and Plant Distribution from the Standpoint of an Idealist (1917-1920), 

 are notable for their penetration and freshness of thought. 



Again, although the prewar years may not have been very eventful scientifi- 

 cally, it was in this period that the foundations were laid for much of the later 

 progress, especially in the increase of knowledge during the years in two fields 

 relating to the distant past. First, it was a time of great activity in paleobotany, 

 and although the more spectacular expressions of this centered in epochs too re- 

 mote to interest the phanerogamist, it produced many important studies on fossil 

 angiosperms. Among these the earlier works of Berry in America (e.g., 1911) and 

 the studies of the Reids in England (e.g., 1908) may be specially noted, the one 

 adding to our knowledge at the earlier end of the angiosperm time scale, the 

 other at the later end. Second, there was a great development in the study of 

 glaciation and its possible consequences, particularly as regards the Pleistocene. 

 It may be claimed that our modern conceptions on this subject date from these 

 years, which saw the publication of Penck and Brlickner's Bie Alpen in Eiszeit- 

 alter (1901-1909) , as well as much of the work of Andersson, de Geer, and others. 



This is perhaps the most appropriate point also for a brief reference to the 

 study of the distribution of cryptogamic plant groups. Because the spermato- 

 phytes reproduce by what are usually macroscopic seeds, because they generally 

 have bulky and resistant plant bodies, and because they have a relatively short 

 geological history, their plant geography has particular values of its own which 

 must not be applied to other groups, though each group has its own relation 

 to this subject. Unfortunately, for the lower plants, much less of the necessary 

 background knowledge is available and the practical difficulties are greater; thus 

 it is fair to say that the only groups of cryptogams which have received the same 

 kind of geographical treatment as the seed plants are the easily collected groups 

 of the ferns and mosses. Christ's standard work on ferns, the Geographie der 

 Fame (1910) dates from these prewar years, but the main work of this period, 

 Herzog's Geographie der Moose, was rather later (1926). Most groups have of 

 course received incidental treatment in the course of taxonomic studies, as for 

 instance in the two editions of the Pflanzenfamilien, but, apart from those 

 mentioned, the only plants which need comment are the lichens, another easily 

 collected group, some of which have long attracted attention by reason of their 

 extraordinarily wide ranges. Indeed, crytogamic phytogeography is largely an 

 untilled field, but it is also one with special difficulties of its own, chiefly inherent 

 in the much longer and more hazy geological history of these plants. 



About the time of the first World War another switch of emphasis became 

 apparent. As already explained, Schimper had long since pointed out that exist- 

 ing floras exhibit only one moment in the history of the earth's vegetation and 

 that in consequence the history of the earth's surface is a matter which must 

 deeply concern the plant geographer. About 1915 several circumstances con- 

 spired to focus attention on this aspect of the subject, so that what had in fact 

 always been its core became crystallized more definitely than hitherto into 

 what has now become known as historical plant geography. Among these cir- 



