RELATIONSHIPS OF METASPERMAE. 605 
or to perish, Those for any reason well-fitted to migrate 
were selected for re-establishment at successively lower lati- 
tudes. Under the relentless overwhelming of the epoch large 
numbers of plants were ejected forever from the Minnesota 
valley, others were so modified in their movement south and 
return to the north that they appear to-day in new specific 
forms, while a large number of new forms, developed princip- 
ally in the group of the Metachlamydez, have been permitted to 
gain a foot-hold. The palms and sequoias have been driven 
out of all this central North American region, the palms to 
maintain a precarious existence in tropical or insular regions, 
the sequoias to their last stand in the limited area of the 
Sierras, where they still continue their losing fight as the 
remnants of an almost extinct race of vegetable giants. The 
enormous size of the ‘“‘big trees” of Calaveras county, has, 
however, one interesting word to tell us of the northern forests 
that were once their home. The very fact of their spread- 
ing their leaves to the light ata height of 300 feet above the 
surface of the earth gives us a hint of the tremendous extent 
to which solidarity of the Tertiary coniferous forests had 
progressed and permits us to understand how stern had 
become the competition for light in view of which such bulk 
was necessary for the preservation of the species. Just as in 
the formidable defensive armor of some extinct armadillo one 
may read somewhat of its struggle with its enemies, so in the 
one hundred meters of solid trunk and in the massive girth of 
a living Sequoia gigantea one may learn of its struggles in the 
ancient forest of Cretaceous and Tertiary times, when its allies 
and competitors were alike more numerous. 
Of all the plants which went south before the first invasion 
of the glacial sheet none showed greater capacity for variation 
and improvement than the ancestral forms of the modern 
dominant family of the Compositae. Such plants as, by per- 
mitting their seeds to fly before the prevalent north winds or 
to attach themselves to the fur of migrating bison, mastodons 
or other animals, had achieved a lower latitude were of: course 
assisted upon their return by the same characters. During 
interglacial time they doubtless established themselves upon 
the till of the Minnesota valley and underwent comminglings 
such as those of to-day. As calculated by Winchell from the 
study of abandoned gorges of the Mississippi valley, the inter- 
glacial period was approximately 9,750 years in length and 
this period as stated by the investigator named, would have 
