276 BOTANICAL GAZETTE [Marcu 
Following is a chapter on “Regeneration,” which begins with a statement 
of Sacu’s theory of formative substances. ‘The reviewer finds much to criticize 
in this chapter, since his own work in this field has led him to very different 
conclusions from those reached by Logs, but only a few points of more general 
interest need be noted here. Special substances are postulated to account for all 
phenomena of regeneration, there is no adequate discussion of nor even refer- 
ence to other hypotheses, and most of the experiments cited are those of LOEB 
and his students. In the discussion of regeneration in plants only the author’s 
experiments on Bryophyllum are mentioned. One would never even suspect 
from reading the book that the problem of regeneration or experimental repro- 
duction had ever received any attention from the botanists. McCaLLum’s 
work is completely ignored. In the case of Bryophyllum, which is discussed 
at some length, Lors’s argument is briefly this: certain substances determine 
the growth of a particular organ, for example, a growing tip, and the growing 
organ attracts these substances. In other words, the substances are necessary 
to make the organ grow, while on the other hand, it must begin to grow in 
order to obtain these substances. These substances are assumed to be in the 
fluids of the body and to be carried by these except in so far as they 
are “attracted” by particular growing tips. If this is the case, how is it possi- 
ble that one growing tip can prevent another, perhaps in its immediate vicinity, 
from obtaining amy of the substance necessary for its growth? But this is 
what Logs assumes and asks us to believe. 
In discussing certain experiments on Planaria, BARDEEN’S earlier conclu- 
sions are accepted and no mention is made of the fact that BARDEEN himself 
showed in later work that they were incorrect, and that more recent work has 
still further demonstrated that the factors concerned, are very different from 
those which Loes postulates. The author’s experiments, made some 25 years 
ago, on the effect of gravity in determining the polarity of the hydroid Amien- 
nularia are described, but there is no discussion or even mention of the fact 
that other investigators have been quite unable to confirm them. 
e flow of substances, assumed by Logs to occur in pieces of the stem of 
the hydroid Tubularia toward one pole or the other as the facts of regeneration 
demand, is entirely without any basis of evidence, and the simultaneous 
regeneration of hydranths or partial hydranths at both ends of a short piece 
with no stem between them presents difficulties to this interpretation. Since 
the short piece produces hydranths and these hydranths occupy its whole 
length, it must have contained enough of the formative substances to produce 
them. If this is the case, why is any flow from other parts necessary for the 
production of a hydranth in longer pieces, as the hydranth-forming region 
must have enough of it to develop a hydranth ? Moreover, if a short piece 
of the stem can transform itself completely into one or more hydranths or 
partial hydranths without the presence of other parts, how can the develop- 
ment of the hydranth be determined by the influence of other parts, as LOEB 
maintains? Further criticisms of this chapter might be made, but perhaps 
