358 
L. H. MACDANIELS 
Pyrus Malus y 
Mature {old tree). Sieve tubes abundant, long and narrow with no clearly defined 
end wall (fig. 27); radial walls covered with closely set sieve plates sometimes 
in two rows (fig. 26); plates of different sizes; pores in different plates of 
nearly the same size, 0.8-1.5 only a few with smaller pores; no sieve plates 
on the tangential walls. 
Companion cells in about one half the sieve tubes. 
Parenchyma of two types: one, the elongate-cambiform with well-developed 
protoplasts; the other longer, containing abundant crystals. 
Prunus Persica 
Mature (fig. 28). Sieve tubes next cambium filled with a blue-staining callus-like 
substance as in Benzoin, very narrow with end walls usually as in type 3; 
occasional end walls with more than one plate, but this exceptional; lattice 
not observed. 
Companion cells not discernible with certainty. 
Parenchyma of slender cambiform type, partially occluded as are the sieve tubes. 
Gleditsia triacanthos 
Mattire. Sieve tubes short, with oblique end wall, with 4-10 narrow sieve plates; 
tubes full of mucilage or protoplasm; lattice not apparent. 
Companion cells not discernible because of heavily staining sieve tube contents. 
Parenchyma of elongate divided-cambiform type. 
Robinia Pseudo-A cacia 
Mature (figs. 30, 36). Sieve tubes of type i, without lattice; sieve plates 35-40^4 
in width. 
Companion cells abundant in corners of sieve tubes. 
Parenchyma of broad conducting type, thin-walled with abundant pitting. 
Mature growing (figs. 31, 32). Formation of rows of parenchyma and of sieve tubes 
from cambium cells of same length. Otherwise no new features. 
Mature root. Differs from mature stem only in having reduced amount of scleren- 
chyma. 
Four-year stem. Sieve tubes of same type as mature but much smaller; small aggre- 
gations of slime near center of each; sieve plates poorly developed, 10-15 
in width; lattice not apparent. 
Companion cells present in most of the sieve tubes. 
Parenchyma very abundant; heavily pitted on the radial walls. 
Four-year root. Very similar to stem of same age but with more storage parenchyma 
and less sclerenchyma. 
Two-year stem. Much as in four-year material, but fewer sieve tubes as compared 
with parenchyma; sieve tubes very small, with poorly developed plates 7-10 jj. 
in width. 
Parenchyma very abundant; packed with starch. 
Two-year root (fig. 35). Like stem of same age but more storage tissue. 
