224 MINUTE ANATOMY OF FLOW'EUINCt PLANTS 



ceous shoot as in a Maple stem of the first year's groAvth 

 (Fig. 376), except that the woody hiyer is commonly tliin- 

 ner, or perhaps reduced to a circle of bundles. The wood 



376. Diagram of a cross section of a \-cry youDg oxoicuous sioin, sljowiii^ six 

 fibro-vascular buDdles. -Ml. Same later, \\itli liimdles increased to 

 twelve. 3T.S. Still later, the wood of tlie btmdles in the form of wedi^es 

 filling the space, separated only by thin lines, or medtillary lays, rnn- 

 ning from jiith to bark. 



all forms in a cylinder' — in cross section a ring — around 

 a central cellular part, dividing- the cellular core williiii, 

 tlie pith, from a cellular bark witliout. As the wdod 

 bundles increase in nitml)er and in si'/c, 

 the}' press upon each other and liccmnc 

 wedge-.s]iaped in the cross section: and 

 they continue to grow from tlie outside, 

 next the bark, so that they become very 

 thin wedges. Bef-wcen the -wedges ;ii-e 

 still tliinner plates ( in cross section lines ) 

 of much compressed cellular tissue, called 

 vieduUarji rai/s, wliich connect the pith 

 -with the bark. The plan of a one-year- 

 old woody stem of this kind is exhibited 

 in the diagran-is. 



520. A\'lien sucli a stem grows on from 





"f year to year, it adds annually a layer of 



;171I. *_'ross secti 



wood : .^, a, ■ i i 



spring wood; wootl outside the [ireceding one, lietwcen 

 /, fall wnod. -that, .^1J^^ ,^l,y ij.,,.]. (Y[g_ 37;,)^ -pi,;^ |^ 



exogenous growth, or outside grdwing, as the name denotes. 

 521. Some new Ijark is formed e\-ery year, as well as 

 new wood, the former inside, as the latter is outside of 

 that of the year preceding. 



