THE PLANT WORLD 



253 



end of the laminae and cuts slantingly down through the petiole, reaching 

 the upper (inner) surface of the petiole at its base. The portion of the 

 petiole remaining is sharp-pointed and remains for a long period, making 

 a most effective spine. (Fig. 3.) 



It is among trees of this group that some 

 very extensive root-systems have been noted, 

 the tips of the smaller roots being found 

 many yards from the base of the trunk. 



IV. Perennials of a spinescent habit with 

 reduced leaves, which do not exhibit any 

 marked seasonal alterations in activity, but 

 continue development more or less slowly 

 throughout the entire year. — The leaf-surfaces 

 of plants of this character are reduced and 

 practicall}' non-existent except upon young 

 plants, the stems and branches being highly 



Fig. 3. Leafy hranchof Fouquifrt'a 

 macdougalii , showing manner 

 of casting of leaves, and forma- 

 tion of spines. 



chlorophyllose, with many 

 marked transpiratory adap- 

 tations of the epidermis. 



The cortical tissues of 

 the stems are sometimes 

 palisaded after the manner 

 of leaves . The spines of this group are generally atrophied branches . Not 

 all plants which share the above characteristics form spines however. 



Koeberlinia, Holacantha enioryi, and Ephedra may be offered as 

 representatives of the group. (Fig. 5.) 



V. Perennials with regular foliar organs protected by varnish, wax. 



Fig. 4. Ephedra sp. growing in gypsum, White Sands, 

 New Mexico. 



