THE STEM. 



11 



The stem is indefinite (c. indeterminatus) when the flowers are borne only on the 

 secondary axes (those springing- from the axils of the leaves), thus appearing to 

 elongate indefinitely (Periwinkle, Pimpernel, fig. 30). 



30. Pimpernel. Indefinite stem. 



81. Columbine. Definite stem. 



The stem is definite (c. deierminatus) when each axis terminates in a flower, 

 and cannot therefore be indefinitely prolonged (Campanula, fig. 159 ; Columbine, fig. 

 31) ; it is aerial when it grows entirely above ground (Stock, fig. 1). 



The rhizome or rootstock (rhizoma) is a stem which extends obliquely or hori- 

 zontally below or on the surface of the ground, the advancing portion emitting 

 fibrous roots, leaves, and shoots, the posterior gradually dying. The rootstock 

 is indefinite (rh. indeterminatum) when it grows by means of a terminal shoot, 

 which lengthens indefinitely, and never itself flowers, but gives off lateral flowering 

 shoots. Thus in the Primrose (fig. 32) the extremity of the rootstock bears a bundle 

 of leaves, in the centre of which is the shoot by which it is indefinitely prolonged, 

 whilst the flowering shoot is developed in the axil of one of the leaves (B). After 

 flowering, the aerial portion of the leaves dies, but the subterranean portion survives, 

 and from its axil spring accessory roots. 



The rootstock is definite (rh. determinatum) when, after producing laterally one 

 or more creeping branches, it rises above the earth, and terminates its existence 

 by a flowering branch. In the Iris (fig. 33) and Arum (figs. 34, 35) the leaf-buses 



