592 
PHANEROGAMS. 
were from the dermatogen forms a cap consisting of several layers of cells, its 
growth being most active in the centre, and diminishing towards the periphery. 
The splitting of the dermatogen into two lamellae usually progresses from the 
centre towards the periphery of the apex of the root ; in the secondary roots of 
Trapa, Hanstein and Reinke state that the reverse is the case^. 
Lateral roots not unfrequently arise in the embryo even before the ripening of 
the seed, in addition to the primary root which we have hitherto alone considered ; 
as, for instance, in many Grasses and some Dicotyledons {e. g. Impatiens, according 
to Hanstein and Reinke, Cucurbita from my own observations). In Trapa natans 
the primary root soon becomes abortive, lateral roots arising at an early period from 
the liypocotyledonary portion of the axis. 
Hanstein and Reinke state that the lateral roots of Angiosperms have their 
origin in the pericambium, in Nageli's sense of the term I Their development was 
found in several plants to harmonise with this. In Trapa natans, for example, it is 
as follows : — A group of cells of the pericambium, which consists of only one layer, 
divides radially; the newly-formed cells elongate in the same direction, and then 
divide tangentially ; the outer of the two layers produces the dermatogen, the inner 
the body of the root. The dermatogen, pushed outwards by the development of the 
body of the root, produces the root-cap in the way already mentioned ; the tissue of 
the body of the root itself which is covered by it becomes differentiated into plerome 
^and periblem. The same process takes place in Pi'stia, and probably also in 
Grasses. Hanstein and Reinke do not find 'anywhere an apical cell which ori- 
ginates the growth, as in Cryptogams, but a group of cells which obey a common 
law of growth.' 
The variation in the size of the embryo in the ripe seed of Angiosperms has 
^ [See the account of the apical growths of roots and of the development of lateral roots which 
is given in the Appendix.] 
^ Compare what was said on Fig. 125, p. 167. 
/ 
Fig. 404.— Diagrammatic representation of the 
formation of the primary root in Monocotyledons and 
its connection with the stem (after Hanstein) ; 7/ sus- 
pensor, h hypophysis, to tv Hne of separation of the root 
and stem, wk layer of the root-cap, d dermatogen, 
pb periblem, plerome. 
Fig. 405. — Diagrammatic representation of the 
same in the case of Dicotyledons (after Hanstein) ; 
I, 2, the first layers of the root-cap, p periblem, dentia- 
togen,// plerome. 
