3 73 



calcareous, clayey and sandy, sour and neutral soils, etc. Instead 

 of ambiguous statements that certain soils are characterized by 

 " pines," " oaks," " bays," " gums," and the like, such as one com- 

 monly finds in soil-survey reports and other publications of similar 

 nature, Dr. Hilgard mentions particular species, not only of trees 

 but smaller plants, and in several cases different forms of the 

 same species.* 



A significant point which he makes (p. 495) is that the " cal- 

 cifuge" plants of pine meadows have as a rule very small seeds. 

 It would be interesting to determine how far this correlation holds 

 with bog-plants in other parts of the world, and with plants of 

 other habitats. 



The second chapter of part 4 deals with the relations of soils 

 to vegetation in other states of the Union and in Europe, as ob- 

 served by the author and a few others who have given attention 

 to the same problems. The statement on page 518 that " Aster 

 Novae-Angliae serves as a reliable guide to high-class lands in the 

 Middle West," when it is well known that this same handsome 

 and easily recognizable species is a common roadside and pasture 

 weed in the washed gravelly soils of New England, is interesting. 

 •Has this species perhaps come into New England from the West 

 in historic times, as many other weeds have done, or are the 



*It is indeed difficult (though perhaps not impossible, as some would have us 

 believe) to draw a sharp line between variations which are due directly and solely to 

 differences in environment, and distinct species which cannot be merged into each 

 other. Dr. Hilgard places in the former class a few pairs of species which were not 

 distinguished by botanists at the time he knew them in the field, but have since stood 

 the test of cultivation side by side, and have been proved distinct by the discovery of 

 additional characters, as well as by their respective ranges. Such pairs are Finus 

 palustris and P. Elliottii (p. 494), Taxodium distichum and T. imbricarhim (p. 

 494), and probably Quercus Phellos ixnd Q. laurifolia (pp. 502, 507). It is scarcely 

 necessary to add that most modern species-makers are inclined to err in the other 

 direction. 



The different forms of post-oaks and black-jacks figured on pages 500 and 501 are 

 indeed remarkable ; and without having seen the originals it would be hazardous to 

 express any opinion on them. The post-oak ( Quercus tninor) has been split up by 

 recent writers into three or -four supposed distinct species, some of which may cor- 

 respond with some of Dr. Hilgard' s figures ; but no subspecies or varieties seem to 

 be recorded for the black-jack {^Queixus marylandica), which Dr. Hilgard finds 

 equally variable. Further study of these forms in the field would be interesting. 



