STEMS. 



143 



S'i 



s'y 



takes place in annuals ; on the other hand, it may make but 

 little growth in extension, so forming a bud, as is common 

 in perennials (Fig. 123). Buds like the last, which are 

 apparently sessile upon the parent axis, are said to be lateral, 

 although, strictly speaking, they are 

 termiual upon very short stems. 



183. — It most frequently hap- 

 pens that new stems arise near to 

 certain leaves. The origin of the 

 stem may be below the leaf, as in 

 many Bryophytes (/, Pig. 132) ; or 

 beside it, as in Equisetacese ; or 

 above it in its axil, as in Monocoty- 

 ledons and Dicotyledons (Fig. 121), 

 and it appears- that in each case the 

 new stem originates shortly after 

 the leaf. 



184. — In Monocotyledons and 

 Dicotyledons there are usually as 

 many new stems formed as there 

 are leaves; exceptionally there may 

 be several new stems (supernumer- 

 ary stems or buds) formed in the 

 axil of each leaf (Fig. 123.) In 

 mosses, ferns, and Conifers, on the 

 contrary, there are by no means as 

 many new stems as there are leaves. 



185. — Earely, new stems (adven- 

 titious stems or buds) arise from 

 the older parts of plants ; thus they 

 may arise from petioles and ribs of 

 some leaves — e.g., Begonia, Bryo- 

 phyllum, etc. ; from the cambium of 

 the cut surfaces of stems — e.g. , 

 elm, willow, etc.; and sometimes in 

 abundance from the fibro-vascular 

 bundles of roots — e.g., Populus alba, cherry, sweet potato, 

 etc. Such structures are always endogenous, as in all cases 

 they spring from some portion of, or near to, the fibro-vas- 

 cular bundles, and break through the overlying tissues. 



Fig. 123,— Branch of the Cher- 

 ry hearing lateral huds ; J', b' A', 

 huds from which lealy branches 

 will develop ; b, b, b. buds from 

 which flowerK will develop. Nat- 

 ural aize.— After Duchartre. 



