ROOT— STEM. 



155 



llillili 



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Fig. 226. — Badiant section of Maple wood {Acer cam- 

 peatris), 1 year old, showing the medullary ray crosBing 

 the stem Irom pith (m) to bark (6). 



I 



to the plant. In many trees it is torn into shreds or ob- 

 literated, making 



them hollow. In 



others it persists, as 



in the Rice - paper 



shrub of China (Fig. 



225) ; here it is 



white, abundant, 



firm, and durable. 



Its lovely cells are 



plainly discernible 



in the paper, which 



is made by cutting the pith into very thin slices. In some 

 Aralias, and in the Pretty-by-nights, 

 there are a few wood- bundles in the pith ; 

 but these are anomalous instances. 



380. The Wood-wedges are deposited 

 in circles, usually one circle each year in 

 cold climates ; so that we can tell the age 

 of the felled tree by the number of its 

 wood-circles. In warm climates two or 

 more circles are often de- 

 posited in a year ; and in 

 many garden vegetables 

 — notably in the beet — 

 many 



circles are formed in a 



few weeks in the root, 



which, as we know, has 



the same growth as the 



stem. In the tropics the 



circles are not so well de- 

 fined, because the stems 



have no winter rest from 



continual growth. The 



wood of the tree-cactus 



forms a continuous stra- fig. 228.-Ebony {d»to™. me»»™). 



turn without rings, though the tree lives many years. In 



the Cycas the wood-rings are few ; yet this is one of the 



most long-lived plants. 



Fig. 227.— Same, 

 gential section ; 

 and hark removed 

 wood-fibre ; JW, me 

 lary rays. 



tan- 

 pith 



; A 



