STEMS 31 



knowledge of them is necessary for the operations of Budding and 

 Grafting described further on. 



In the stems of Monocotyledons we find a different structure, the 

 most striking feature being the absence of real pith, wood, and bark. 

 There is no cambium layer, and consequently no concentric rings of 

 wood and bark as in Dicotyledons, and the fibrous bundles are chiefly 

 collected on the outer portions of them, and give them the hard texture 

 so well known in the stems of Bamboos and Canes. 



As it is the presence of the cambium layer which enables grafting 

 or budding to be done at all, it therefore follows that these operations 

 cannot be performed satisfactorily on Monocotyledons which have 

 no cambium layer in their stems. 



KINDS OF STEMS 



Stems are usually regarded as being above the soil, but there are 

 certain modified kinds which perform their work beneath the surface, 

 and are popularly looked upon as roots. 



Those above the surface are classified as follows : — 



1. Herbaceous. These are stems which die down to the ground 

 every year after blooming, as in the case of most hardy herbaceous 

 perennials (see list, p. 86). 



2. Sub-shrubby, more or less woody below but herbaceous above. 



3. Shrubby, arborescent, or arboreous, woody, and living from year 

 to year, and attaining considerable size as in the case of trees and shrubs, 

 a list of which is given at p. 107. 



Stems assume various directions in growth, some being erect and 

 ascending, others more or less trailing or prostrate on the ground, 

 others creeping and developing roots at the joints, where they touch 

 the soil ; and others cHmbing or twining by tendrils, as in the Passion 

 Flower and Virginian Creeper ; by twisted leaf -stalks, as in the Clematis, 

 or by aerial rootlets, as in the Ivy. 



Stolons are stems or branches which rechne on the earth and take 

 root. Many plants are naturally increased in this way and the process 

 of layering was no doubt suggested by seeing stems throw out roots 

 when in contact with the soil. 



An Offset is a short stolon with a tuft of leaves at the end, from 

 which roots also develop, as seen in the common Houseleek. 



Bunners, as in the Strawberry, are similar in their nature, being 

 long slender stolons which when fully grown develop roots at the tip, 

 and afterwards buds and leaves to form a new plant. 



Tendrils are branches modified for climbing purposes, and are either 

 simple or branched, but are useless for propagating purposes. 



