PLATE XLI. 



Townsendia exscapa. 



Fig. 16. Medullary-ray cells, cross section. X 650. 

 Fig. 17. Medullaiy-ray cells, longitudinal section, x 650. 

 Fig. 18. Phloem cells, cross section. X 650. 



Fig. 19. Phloem cells, longitudinal section: a, cambiform cell; b, undi- 

 vided mother cell of the sieve tubes, x 650. 

 Fig. 20. Cross section of root, showing the distribution of tracheids. 



X 115. 

 Fig. 21a. A bleached leaf, showing its method of venation, x 121/4. 

 Fig. 21b. Midrib of leaf, cross section, showing: a, phloem cells; b, 



tracheids; c, wood parenchyma cells. X 215. 

 Fig. 22. Portion of a bleached leaf, showing the details of venation. 



X 115. 

 Fig. 2.3. Phloem cells as seen in a longitudinal section of the midrib of 



a leaf: a, cambiform cell; b, undivided mother cell of the 



sieve tubes. X 650. 

 Fig. 24. Cutinized epidermis of leaf, cross section: a, cuticle; b, cutin- 



ized portion of wall. X 650. 

 Fig. 25. Palisade cells, surface view: c, intercellular spaces; d, palisade 



cell. X 650. 

 Fig. 26. Spongy parenchyma cells, surface view. X 650. 



