INDEX. 



47i 



Weeds, 403 

 Willow, 348 



order, 396 

 Wilting, cause of, 22 

 Winged fruits, 365 

 Witches' broom, 226 

 Wood, heart, 81 



oak, 80 



pine, 331 



sap, 81 



sections, 78, 79 



spring, 77 



summer, 77 

 Woodwardia, 295 

 Work of plants, 15 



Xanthidium, 168 

 Xerophytes, 35, 40 

 Xylaria, 216 

 Xylem, 52, 64, 65 



Yamanouchi, 194 

 Yeast, 206, 207 

 Yucca, 386 



Zamia, 322, 323, 324, 326 

 Zoospore, 136 

 Zygnema, 165, 167 

 Zygnematales, 165 

 Zygomorphic, .354 



