182 



PLANT LIFE. 



Stems, however, the elongating part may measure twenty ore\-en 



fifty centimeters, and in rare cases 

 much more. Figure 1 84 shows a 

 root, .-l,npon "wliose surface marks 

 were made i mm. apart. Twenty- 

 four hours later the root presents 

 the appearance of B. Only the 

 tissues in the first fi\e spaces were 

 capable of elongation. The others 

 had passed into the third phase. 

 The second and third millimeters 

 grew most in length. The growing 

 regions of stems may be deter- 

 mined in the same «'ay. 



259. Tension of tissues. — The 

 different tissues in any organ usu- 

 ally do not grow at an equal pace, 

 and consei[uently certain tissues 

 are under strain, while others are 

 compressed. The curled and 

 crinkled leaves or the cur\ed cap- 

 , , sules of mosses illustrate this in- 



FlG. 184. — --/. a ynullg rnot rpf tile l>L-n 



marked mth fine lines of chinuse e(iuality. It maybe ijresent, how- 

 ink into 13 spaces of i millimeter ^ ^ 



each. jS, the same root, 24 hours ever, w'itliout manilesling itself in 



later, showing; elongation only in ■- 



terminal 5 millimeters Tlierateof external forui. I'llis general COU- 



growth IS greatest in the 2d and 3d ^ 



millimeters and slo^y in the ist, 4th, dltioil is kllOWlias \ht tension of 



and 5th. JMagnitied 2 tliaiii. — Alter 



i*""'^- lissiit's. If the ra[iid]y growing 



flower-slalk of the dandelion or tlie leaf-stalk of rhubarb 

 be carefully sjilit lengthwise the parts will < in\e or c\ en curl 

 outward. Se|>arating the inner and outer tissues of a "\oiing 

 elder shoot and carefully measuring ihcin shows that the 

 inner tissues elongate and the outer actualh' shorten. The 

 experiment, therctore, shows that the inner tissues reallv 

 grew more ra|)idly than the outer, but were comi)ressed in 



