6 
Review. 
means of a vegetative growing point producing lateral leaves, can 
only be modifications of the same mode of development, and 
cannot be due to different morphological qualities of the same 
embryonic shoot. In acroblastic branching the leaves, although 
they form the organic terminal portions of each “ Sprossglied,” arise 
laterally on the plant because they are retarded in their development) 
not growing out until after a second “Sprossglied” does so; this 
latter being much stronger than the leaf of the last “ Sprossglied ” 
immediately behind it, necessarily overtops that leaf and becomes 
terminal. Acroblastic is more rapid and stronger than pleuroblastic 
branching and hence has been adopted in almost all plants; the 
former has been derived from the latter. Dichoblastic branching is 
intermediate between aero- and pleuroblastic, and possibly preceded 
the former; it apparently occurs in the early development of the 
embryo of Pteridophytes. 
In Chapter III. the origin of stems with mericyclic “ Spross- 
glieder ” is considered. Here it is shewn (and this can only be 
clearly understood, perhaps, by reference to the diagram given) that 
an acroblastic stem with mericyclic “ Sprossglieder ” can be derived 
from a pleuroblastic one by vertical fusion of the holocyclic “Spross¬ 
glieder ” of the latter above and below, and this fusion occurs 
congenitally in every stem; this is seen in the mosses. The pro- 
tomena of a moss possesses holocyclic “ Sprossglieder; ” in the 
moss-plant the latter are mericyclic where each segment cut off 
from the apical cell does not extend entirely across the stem, but 
abuts on the wall of the last segment. The apical cell of a 
cryptogam corresponds with the formation of the three wedge-shaped 
segments of the mericyclic “ Sprossglieder ” of a plant with J phyllo- 
taxis. An apical meristem, which as in the Fern, cuts off a number 
of segments from the apical cell before the first leaf is formed, as 
also the layered apical meristem of Phanerogams consist of more 
than one “ Sprossglied ” ; the apical cell has given rise to the layered 
condition by means of early divisions in its segments, so that the 
“ Sprossglieder ” have become quite obscured, but are nevertheless 
present. Hence the origin of mericyclic stems from holocyclic, 
which is distinctly perceived in the mosses and Pteridophytes, has 
become obscured (by further complications connected with cell- 
division) in the Phanerogams. 
Chapter IV. contains a setting-forth of all the numerous 
