ae 
1907] CURRENT LITERATURE 65 
and compares these structures with one another. For example, the foliage leaf is a 
well-defined organ which can be recognized at a glance; but it requires some study 
to understand that the scales on the bud and around an onion, and also some forms 
of spines and tendrils are morphologically leaves, that is, are leaves variously modified. 
Because all of these structures are related to one another, they are called homologous, 
and morphology studies the homologies or relationships of organs. Comparative 
morphology is one of the interesting subjects of biological pm since it furnishes 
the basis for the established belief in the evolution or development of the higher plants 
and animals from simpler forms. 
Furthermore, before beginning the study of types, the author says concerning 
the process of evolution: 
The forms and groups split up into divergent lines which constantly se off, and 
are still giving off, new shoots. Thus from a number of trunks in the nning there 
have been derived a salted of smaller branches, and from these in turn ria arisen 
countless twigs. It is impossible to construct bears these genealogical trees, 
because the species now living occupy the position of buds on the structure, so 
relatively low down and some at the highest points, as all at the ends of their respec- 
tive lines of development. 
If the student has come to the second part after a careful study of the first, 
the foregoing paragraphs possibly may be significant to him. If, as a suggested 
possibility in the preface, the student should begin his study with the second part, 
such statements must prove bewildering. Presumably he knows little or nothing 
of the terms used nor of the structures or organs of which they speak, and it 
would seem that attempts at this point to show the significance of “comparative 
morphology” would be lost. Also, within the first dozen pages the difficult topic of 
photosynthesis, with the outlines of the chemical formulae involved, is presented 
within the limits of a page. Upon a clear understanding of this topic the signifi- 
cance of much of the subsequent work must depend, and if the chemistry of the 
process is presented at al!, it should be in such a form as to be understood by 
immature minds. 
The number of types used and the detail with which their part in the evolu- 
tionary story is presenied are far greater than has yet appeared in a text designed 
for elementary use. Indeed few texts used by college classes are so inclusive. 
It is difficult to understand just how elementary students are going to see the 
significance of such discussions as (1) that of reduction of chromosomes in Coleo- 
chaete as related to ciaims of a sporo ophytic generation in that plant; (2) of the 
“Imperfect fungi;”” (3) of the ‘Evolution of the flower;” (4) of frequent refer- 
ence in brackets or otherwise to highly specialized genera that are unexplained 
in the text. The author suggests that such topics be omitted if thereby the 
teacher’s ideas are met in a better way; but in many cases subsequent discussion 
involves a knowledge of these features. A summary at the end of each group 
Serves to simplify many of the more difficult points. 
A highly commendable feature is the introduction of such topics as “Public 
health, ” and ‘Fossil plants and coal.” Frequent suggestions as to economic 
aspects of plants under discussion add muck to the value of this part of the book, 
