638 
PHANEROGAMS. 
root ceases, adventitious roots become intercalated among the lateral roots already 
formed, and like them, grow vigorously, and may themselves produce lateral roots 
of higher orders. A strong root-system is thus produced with the primary root of 
the embryo for its centre, which endures as long as the stem itself. By the subse- 
quent increase in thickness the primary stem (as well as its branches) assumes the 
form of a slender upright cone, the base of which rests on the base of the inverted 
cone formed by the primary root which has also increased in thickness. While 
these processes, which are here described in their main outlines, take place almost 
invariably among Conifers, a number of deviations occur, on the other hand, 
among Dicotyledons similar to those which have been spoken of under the head 
of Monocotyledons. The primary axis may die soon after germination or at the 
end of the first period of vegetation, the primary root often perishing as well, while 
the axillary shoots of the cotyledons or of subsequent leaves continue the life of the 
individual. Thus, for example, in the Dahlia, a strong adventitious root is given out 
laterally from the hypocotyledonary portion of the axis at the close of the first period 
of vegetation of the young plant, and swells into a tuber; the primary root-system 
and the portion of the axis above the cotyledons disappear, and there remain only 
for the continuance of the life of the plant the new tuberous root, the hypocoty- 
ledonary portion of the axis, and the axillary buds of the cotyledons. The process 
is still more striking in Ranunculus Ficaria, where, after the development of the 
primary root, a tuberous lateral root is produced below the primary axis of the 
embryo, sheathed by a coleorhiza, and maintains its existence together with the 
axis, while the primary root and the first leaves perish. Among the numerous 
cases belonging to this category may be mentioned also Physalis Alkekengi, Mentha 
arvensis, Bryonia alba, Polygonum aniphibium, and Lysimachia vulgaris ^ The pro- 
duction of bulbs also occurs among Dicotyledons (as in species of Oxalis), though 
not so commonly as among Monocotyledons ; of more common occurrence are 
tubers or swellings of underground branches, stolons, or rhizomes of greater or less 
thickness. The greater number of Dicotyledons have perennial underground roots 
or stems which send up periodically leafy and flowering shoots that die at the end 
of each period of vegetation. In all such cases, where the primary root-system 
of the seedling perishes, new roots are repeatedly developed from the stem ; and 
the power possessed by most Dicotyledons of producing adventitious roots from the 
stem, especially when kept moist and dark, enables them to be reproduced to almost 
any extent from branches and portions of branches. Some species climb, like the 
Ivy, by roots put out regularly from the weak stem which requires a support ; others 
send out runners to a distance, on which the bud forms a new plant, as in the Straw- 
berry, the stem which is thus formed putting out roots. The order of succession of 
new roots from the stem is in general acropetal, but they do not usually make 
their appearance except at a considerable distance behind the growing bud ; many 
Cactaceae however not unfrequently produce them close below it. 
ThQ Mode 0/ Branching. The normal monopodial branching is axillary; the 
lateral shoots are produced in the angle which the median line of the leaf forms 
' The above is taken from Irmisch's detailed descriptions in his Beiträge zur vergleichenden 
Morphologie der Pflanzen, Halle, 1854, 1856; Bot. Zeitg. 1861 ; and elsewhere. 
