SHOOTS 



75 



55. The rootstock type. — This is proL- 

 ably the most common form of snhter- 

 raucan .stem. It is elonijatcd, as are foli- 

 age stems, and lience the scale leaves 

 are well separated. It is prominentl}' 

 used for food storage, and is also admirably 

 adapted for subterranean migration (see 

 Fig. OS). It can do for the plant, in the 

 way of migrati(ni, what prostrate foliage- 

 bearing stems do, and isin amore protected 

 position. Advancing beneath the ground, 

 it sends up a succession of branches 

 to the surface. It is a very etticient 

 method for the '■'spreading" <if plants. 

 and is extensively used by grasses in cov- 

 ering areas and forming turf. The persist- 

 ent continuance of the worst weeds is often 

 due to this habit (see Figs. 60, To). It 



is impossiljle 

 1 r e m o v e 

 all of the 

 indefinitely 

 branc h i n g 

 r o t g t o c k s 

 from the soil, 



and any fragments that remain 

 are able to send up fresh crops 

 i)f aerial branches. 



53. Alternation of rest and 

 activity. — In all of the three 

 stem types just mentioned, it 

 is important to note that they 

 are associated with a remark- 

 FiG. 66. A bulb, made up ot overlap- able alternation between rest 



ping scales, which are fleshy on j^j^^ vigOrOUS activitV. From 



account of food storage. — After 



Grat, 



Fio.ij.!). Branch buds 

 of elm. Tlireebuds 

 |y() uitli their o^■er' 

 lapping scales are 

 sho^\n, each just 

 above the scar (b) 

 of an old leaf.— 

 After Behkens. 



the branch buds the new leaves 



