196 



PLANT LIFE. 



because iisuall}- illuminated from one side. Plants kept in 

 darkness ha\"e their leaves irreyularh' placed. 



286. {h) Combined movements due to variations in the 



Fin. i,j2 — A shoot of thorn-.ijiple or " jiiiisnn '" weed, showing imperfect Ie.lf mosaics 

 of t.^ll plants fonned upon the s.atne plan as in rosettes (Itg. ig3). Chie-se\'enth nattiral 

 si/,e. — .After Kerner. 



amount of light or heat or hotli are especially exhibited b)' flow- 

 ers, whose opening and closing are frequently determined 



Firj. IQ3. — A rosette of leaves of a W\\\\i\\\^:x {Caitjf'aauia fusil/a), showing length- 

 ening nf petioles of lower leaves so as to earn.' blades from nnder u]-tper IcaA'es — 

 After Kerner. 



therchw W'itli sonic planis the predominant stimulus is heat; 

 witli others, light. Closed llowers of tlie tulip or croi iis may 

 he made to open in 2 to 4 minutes b)- raising the temperature 



