. A textbook of botany for colleges and universities ... Botany. STEMS 671 adventitious roots and erect shoots develop at various points on the radiating stems. The older parts gradually decay, so that the branches become isolated as separate plants; consequently there is an increase in the number of individuals as well as in the space occupied. In this phenomenon of vegetative reproduction, however, it is not a matter of particular importance whether or not the actual number of individuals is increased by isolation. The imp>ortant matter is the occupation of new space, for in any case a rh
. A textbook of botany for colleges and universities ... Botany. STEMS 671 adventitious roots and erect shoots develop at various points on the radiating stems. The older parts gradually decay, so that the branches become isolated as separate plants; consequently there is an increase in the number of individuals as well as in the space occupied. In this phenomenon of vegetative reproduction, however, it is not a matter of particular importance whether or not the actual number of individuals is increased by isolation. The imp>ortant matter is the occupation of new space, for in any case a rhizome colony or rhizome complex represents a number of potential individuals, as is well shown after the plowing of a field partially occupied by such plants ( thecouch , Agropyrum repens); the rhizomes are dislodged and broken and the scattered frag- ments form new centers of migration. The great advantage of rhizomes as organs of propagation is due partly to their horizontality, partly to their elongation, and partly to the fact that they are soil structures and thus are able to invade regions already oc- cupied. Seeds fall in numbers every- where, but hundreds die where one develops, because of the difficulty of striking root in ground already preempted; even plants with runners propagate with difficulty where vege- tation is dense. Rhizomes, however, penetrate the soil of forests or of grasslands scarcely less readily than that of open grounds. The advantage of the rhizome habit is well illustrated in fields that have lain fallow; during the first year, annuals usually dominate, but little by little rhizome plants and other perennials increase their area, invading the space previously occupied by annuals, until finally all of the latter are Fig. 983. —^ A rhizome of the Solomon's seal (Polygonatum biflorum); note the tuberous enlargements of the rhizome with the conspicuous scars is) left by the fall of the erect stems of previous seasons; r, adventit
Size: 1410px × 1773px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
