AB vim. a ee) ee te Wa fe ¥.« Ata, a. et nt ow , 
r See ue yi 5 44 | Bt! - OE aa 2 so ype ley i 4 We as 
aoe rere! ye x f. bot AP J : \ x 
A fi Sink ares Pe arsatp 
bens “The External Form of Plats. v3 nie 
/ . 
| The aérial roots P Ropical Or chids, Be hthi [and Aroids] depend from 
the stem and branches, and in many cases never reach the ground. 
hie floating primary root of Z7apa, which germinates while lying on the 
ground, at first ascends, and remains in that direction. The aquatic roots 
of floating plants like Zemmna never attempt to become fixed in the 
ground ; or, as in the case of Cicuta, assume a totally different appear- 
ance. The ‘haustoria’ of parasitic plan‘s, finally, penetrate into the 
stem of their hosts, and feed on their sap. The characters which 
include all roots, and distinguish them from stems, are the absence of 
leaves, and the presence of a root-cap at their extremity. | 
By the primary root is meant that which 1s formed by. 
the downward elongation of the axis of the embryo, and which 
Fic. ror.—Diagram of Fic. 102.—Fusiform root Fic. 103.—Napiform root 
a tap-root. : of the carrot. of the radish. 
is therefore in a line with the stem. It is called a ¢ap-root 
(Fig. tor) when it is thicker than the branches which pro- 
ceed from it; and may then be /fuszform or spindle-shaped 
(Fig. 102), zapiform or turnip-shaped (Fig. 103), premorse, 
7.é€. suddenly ending with a blunt point, as if bitten off, as 
in Llantago major |or Scabiosa succisa), lt tform (Fig. 104), 
or cylindrical, 
Secondary or lateral roots are those which spring laterally 
from the stem [or from the primary root], as the clasping roots 
ofivy. In many plants in which the primary root remains 
™ 
