STEMS AND THEIR VARIETIES 



5S 



Ex. 29. — Kxamhie the thorns upon the hawthorn, .sloe, wild plum, wild pear, 

 and buckthorn. Note their origin in the axils of leaves, and that some of 

 them bear buds and leaves. 



Ex. 30. — Examine the origin of the runners upon strawberry jjlants, mouse- 

 ear hawkweed, and creeping crowfoot. Observe the position of the leaves 

 and buds upon the runners. 



ii. Underground. 



Stems within the soil sometimes resemble roots, but they can 

 be distinguished from the latter by the possession of leaves and 

 buds, and by their originating in the axils of leaves. 



(a) A rhizome or ' rootstock ' is an underground shoot, which 

 grows more or less horizontally. Adventitious-roots arise at the 

 nodes, and the internodes may be long or short, thick or thin, so 



1 



Fig. 22. — I. Diagram illustrating growth of an indefinite rhizome. A to B, 

 indefinite primary axis which remains below ground permanently, i, 2 and 3, 

 lateral branches of A B which come above ground. 



2. Diagram illustrating growth of a definite rhizome. A to B, definite 

 primary axis which has flowered and decayed away ; 2, a branch from the 

 primary axis coming above ground ; 3, a branch from 2 ; 4, a branch from 3. 

 The whole stem from ^ to C below ground is a sympodium or false main-axis. 



that the general appearance of a rhizome is variable, those of 

 couch and other grasses being long, thin straggling shoots, while 

 in iris, hop and other plants they are thick and fleshy. When 

 leaves are present, they are generally reduced to the form of 

 membranous scales. 



Rhizomes may be indefinite or definite in growth ; in the 

 former case, the true and main axis continues to grow at its 

 tip, and always remains below ground ; the parts which come 

 above ground are secondary or lateral branches, which arise in 

 the axils of its scaly leaves (i, Fig. 22). Most rhizomes are, how- 



