1gog| CURRENT LITERATURE 153 
succession of events in the life-history of a plant is no more normal than any 
other succession of events that may be produced by altering the external condi- 
tions. Like Kiess, therefore, he is obliged to discard the word normal or place 
it in quotation marks. To the reviewer such a viewpoint seems fundamentally 
sound, and it has the added attraction of throwing open to experimentation all 
the phenomena of development, including those that have been referred to hered- 
ity or mysterious internal causes. In harmony with this fundamental principle, 
illustrations are given of the omission of individual stages from a developmental 
series, the transposition of two such stages, and the retention of a given stage, if 
the conditions favorable to another are not forthcoming; even the juvenile 
stages may be retained through life in many instances, if the external conditions 
are favorable thereto. On the other hand, there are cases where juvenile forms 
bear flowers, the intervening stages being skipped. 
The body of the book consists of four chapters, dealing respectively with the 
influence of external and internal conditions on leaf form, the conditions deter- 
mining variations in the development of main and lateral axes, regeneration, and 
polarity. In all of these chapters there is a wealth of detail of the utmost value 
to students in experimental morphology and to those desiring a bibliography of 
these subjects. Not only is the literature summarized, but there are many new 
and suggestive experiments mentioned here for the first time. In the chapter 
on leaf form, heterophylly in xerophytic species of Veronica and in such amphib- 
tous plants as Limnophila plays an important part. Mutation in some ferns 
is definitely referred to the operation of external factors. Plants with orthotropous 
and plagiotropous shoots are found to belong to two categories. For example, 
lateral branches of the spruce (Picea excelsa) become orthotropous if the termi- 
nal shoot is removed, while such a reaction does not occur in Araucaria; the 
former illustrates lability, the latter stability. The same chapter contains some 
very interesting data concerning variation in flowers and inflorescences. Of 
SR aps it seems not to get down to fundamental principles. Throughout the 
the work nutrition is regarded as a dominant external factor. Whileitis true that 
it is as yet impossible to resolve nutrition into its components, it is at least better 
pa to do so than to assume that ition is reall thing definite, or even 
a te. To many of us the work will be more useful as a summary of facts 
as an explanation of the conditions underlying them.—HENry C. COWLES. 
ally tt > 
