Sacks Lectures. 87 
transverse walls have been added. Thus the plant is divided into 
chambers, not built up of cells. 
In the treatment (p. 152) of the higher Fungi, the physiological type 
again comes into prominence. The author describes the closely- 
packed epidermal tissue, and points to the bundles ‘ formed of parallel 
elongated elements- ’ running in the fundamental tissue, which he says 
are 4 to be regarded as the rudiments of a vascular bundle/ Without 
wishing to detract from the interest of this discussion, we must point 
out that it is liable to misinterpretation. The student will be inclined 
to suppose that the vascular bundles of the higher plants are, so to 
speak, the lineal descendants of the strands of mycelium in the Fungus, 
which is far from being necessarily the case. Such points as these, 
and there are others of a similar kind, make us doubt whether the book 
is well fitted for uninstructed readers, though we give it all praise for 
its vividness and suggestiveness which makes it delightful reading to 
advanced students of Botany. 
The remainder, fully three-fourths, of the volume is devoted to 
Physiology, and is divided into the sections ‘ External Conditions of 
Vegetable Life, and the properties of plants' — ‘ Nutrition ’—‘Growth ’ 
— ‘ Irritability ’ — Reproduction.’ One of the most masterly of these 
sections is the first, and it is a good example of the broad general 
treatment in which the author delights. He points out (p. 19 1) that 
all the phenomena of life arise from two factors : ‘ on the one hand 
from the structure transmitted from the mother-organism, and on the 
other, from external forces working on this structure/ He then goes 
on to show how great are the difficulties which meet the physiologist in 
the investigation of the first factor, since the most radical physiological 
distinctions give no outward and visible sign in the way of structure, 
but depend on differences in the ‘ invisible smallest particles of matter/ 
This leads on to the interesting discussion, in Lecture XIII, on the 
molecular structure of plants; while Lecture XII, dealing with the 
second factor (the action of the environment), treats of the general 
relation of plants to heat, light, electricity, etc., and completes this 
admirable study of the biology of plants. 
It would take us too far to attempt to follow the author through 
even a selection of his forty-six lectures. We rejoice that under the 
heading ‘ Irritability ’ Professor Sachs places Geotropism and Helio- 
tropism in the same category, an arrangement far preferable to that 
followed in the ‘ Text-Book.’ This point- of view was we believe first 
