650 DEFINITION AND CLASSIFICATION OF STEMS. 



than the continuation of the basal portion of these leaves. As in so many similar 

 instances, the whole matter finally ends in an unfruitful strife of words where 

 everyone is in the right. The simplest way is to regard as a stem every axis of a 

 plant which, when developed, always bears geometrically-arranged leaves, and to 

 avoid speculations as to whether this stem is to be considered as an independent 

 structure apart from leaves, or as a combination of their basal portions. 



Whatever theory we may hold of these relations, not only the form but also 

 the function of the leaves borne by the part of the stem in question must be 

 regarded as the predominating factor in the portrayal of the stem structure — 

 especially when the peculiar construction of a given stem is to be explained by the 

 special duties assigned to it. 



There is no plant in which the stem is developed quite uniformly from the base 

 to the apex. We can always distinguish in it stories following one above the other, 

 each of which is fashioned in accordance with the work it has to perform. Just as 

 in buildings the underground walls, which serve as the foundation of the whole and 

 usually also as a store-room for food, &c., exhibit quite a different kind of structure 

 from the upper stories which are inhabited, and where kitchen, bed-rooms, airy 

 parlours and passages are found, so, in one and the same plant, different plans of 

 construction are realized according as to whether the part in question bears coty- 

 ledons, scale-leaves, foliage-leaves, or floral-leaves, the functions of which are so 

 extremely various. It therefore seems most natural to classify stems as hypocotyls, 

 scale-leaf stems, foliage-stems, and floral-stems. 



There is not much to be said about the hypocotyl {fundamentwm). The little 

 that is of interest has been stated already in describing the cotyledons. After it 

 has drawn the cotyledons from their envelope and has straightened itself, the 

 hypocotyl undergoes no altei-ations worth mentioning and is only of importance in 

 that the bud of the main shoot is developed from its apex, and the food absorbed 

 by the radicle is conducted by its means to this bud. 



The stem bearing scale-leaves (subex) is usually so short in its first stages that 

 its leaves lie close packed above one another, the upper ones being wholly or for the 

 most part covered by the lower. In many instances it remains very short throughout 

 life, and is then termed a reduced axis or " short branch ". In others it extends and 

 elongates so that its leaves are separated, and it is then called a " long branch ". It 

 may happen that one of these scaly stems is at intervals sometimes a long and some- 

 times a reduced axis; it may then be compared to a string, in which knots have 

 been tied at certain distances. In the case of a scaly stem passing over into a 

 foliage-stem beset with green leaves, the former usually has the form of a reduced 

 axis. It is then either flattened or disc-like, or it may be of a shortly cylindrical or 

 conical form. If it is beset with large scale-leaves and is considerably thicker than 

 the leafy foliage-stem into which it almost directly passes, we speak of it as an 

 abbreviated stem. This, together with its large and hollowed scale-leaves, is termed 

 a bulb (bulbus); it is almost always underground, and its axis is vertical, as, for 

 example, in lilies, tulips, hyacinths, and stars of Bethlehem. 



