454 BOTANICAL GAZETTE [JUNE 
SETCHELL’® gives an account of regeneration among kelps. He distin- 
guishes between physiological and restorative regeneration, applying the terms 
in the same sense as used by Morcan. In physiological regeneration he notes 
two kinds, continuous and periodic. In the former the continuous growth 
of the meristematic tissue at the base of the blade keeps pace with the constant 
breaking off at the tip due to wave action, and so the blade retains a constant 
length. In other species this growth is periodic, occurring in the spring and 
inthe autumn. The growth of a new blade lifts the old one from the top of the 
stipe and it is rapidly eroded, the new one thus taking its place. Restorative 
regeneration involves the development of new branches and occurs as a result 
of wounding. If the stipe is broken off a new blade is formed at its apex. Wounds 
along the surface of the stipe result in new blades arising at the points. A ver- 
tical wound at the tip results in a splitting of the blade and the appearance of 
forking. The observations are followed by a discussion in which the author 
contends that the phenomena of regeneration are to be explained best by the 
assumption of a flow of materials toward the parts concerned. He does not 
consider it necessary to assume a special organ-forming material, the impor- 
tant thing being the control of the flow of already organized food materials. 
This control of the food substances is due to certain cells being able to exert 
a stronger ‘‘pull” upon them than others. 
As this idea is so commonly used in explanation of regeneration, the reviewer 
cannot forbear remarking that it removes one difficulty only to incur a greater 
one. Soluble food materials, in common with all other diffusible solutions 
in plants, move toward the region of least concentration, and if there is a more 
rap:d flow of substances toward any region, it indicates that these are being 
taken out of solution there, either by being used or otherwise transformed. The 
more active the use, the lower will be the concentration, and the more active the 
flow will tend to be toward that point. The increased activity of the cells, 
either in using up by growth or otherwise transforming the food substances, 
must precede any special flow (that is, apart from a general diffusion in all direc- 
tions) of these substances into any particular region. The movement, or, if pre- 
ferred, the ‘‘flow” of soluble substances (other than a general diffusion) toward 
special cells is necessarily a result and not the cause of their activity. . 
MirHe”’ has used an interesting method of studying the behavior of isolated 
cells, especially in their relation to polarity. When a tissue is plasmolyzed, 
the continuity of the protoplasm is broken and the protoplasts become separated 
from one another. In this way a plant may be divided into its individual cells, 
and the behavior of these, each acting independently, can be studied. MreHE 
used this method on a marine Cladophora. The plants were plasmolyzed in 
16 SETCHELL, WILLIAM le Regeneration among kelps. Univ. Calif. Publ. 
Bot. 2:139-168. pls. 15-17. 
17 MIEHE, Huco, Nia. Regeneron und Polaritit isolierter Zellen. Ber. 
Deutsch. hon Gesell. 23:257-264. pl. 4. 1905. 
