SPERMATOPHYTES—ANGIOSPERMS 
295 
Smilax shows the radial arrangement, with a large number of poles 
and a very highly differentiated endodermis. The origin of secondary 
xylem and phloem is well shown in Sambucus nigra. Vida Faba 
shows very clearly the origin of secondary roots. Pislia stratiotes, 
although not so generally available, is splendid for showing the 
origin of secondary roots. The arrangement of cells in the young 
Fig. 105 .—Sparganium eurycarpum: photomicrograph of transverse section of young root; 
fixed in chromo-acetic acid and stained in Bismarck brown; Cramer contrast plate; 16-mm. 
objective; ocular X4; no Abb6 condenser; yellowish-green filter; camera bellows, 1 meter; 
exposure, 8 seconds. X90. 
roots of aquatic or semi-aquatic plants is often extremely regular 
(Fig. 105). 
The leaf .—Young and tender leaves should be fixed in formalin 
alcohol and cut in paraffin. Cut sections freehand whenever there 
is sufficient rigidity. Resort to pith only when necessary. In 
cutting sections of a leaf like that of Lilium , lay one leaf on another 
until you have a bundle of them which will be nearly square in trans¬ 
verse section. Wrap the bundle with string for about 15 mm.; cut 
