14 



PART I. — ORGANOGRAPHY. 



which, on coming in contact with the soil, takes root, and ulti- 

 mately gives rise to a new plant. The Currant and Raspberry 

 afford examples. 



The Sucker is an aerial shoot that springs from an under- 

 ground branch. This form of stem is also illustrated in the 

 Raspberry. 



The Offset is either a short sucker or a short stolon, and is 

 illustrated in the common Houseleek. 



The Runner is such a creeping and rooting stem as that of 

 the Strawberry, Fig. 19. 



Fig. 19. — Strawberry plant producing a runner. 



Fig 20. — Branching thorn 

 of the Honey-locust. 



The Thorn or Spine is a stem modification which is hard, 

 pointed and destitute of leaves, or nearly so ; for example, the 

 thorns of the Honey Locust, Fig. 20. Not all spines, however, 

 are modified stems ; some are modified leaves or portions of 

 leaves. 



Underground Stems. 



The stems so far described are all aerial or above ground, 

 but there are also subterranean ones, which mimic the habits of 

 roots. They may readily be distinguished from the latter by the 

 fact that they bear scales or scale scars, in the axils of which 

 buds not infrequently occur, and also by the fact that the grow- 

 ing-point is situated at the apex instead of just back of it. Its 

 growing end is enveloped in scales, the representatives of leaves; 

 it, therefore, like the above-ground stem, possesses a terminal 

 bud. Various kinds of subterranean stems are distinguished, the 

 more important of which are the following : 



The Rhizome is a creeping, underground stem, which grows 

 horizontally or obliquely, is more or less scaly or marked with 



