HISTOLOGY OF PHLOEM IN WOODY ANGIOSPERMS 
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One-year stem, one-year root. Sieve tubes very small with poorly developed sieve 
plates; would not be recognizable except for dark-staining slime; very similar 
to parenchyma in size and shape. 
Ailanthus glandulosa 
Mature (fig. 29). Sieve tubes collapsed except close to cambium; large, very thin- 
walled, with usually a single transverse sieve plate; rarely 2-3 sieve plates. 
Pores of sieve plate very large; lattice not present. 
Companion cells probably present but not observed on account of condition of 
material, 
Parenchyma of conducting type; very thin-walled, in strands accompanying 
the sieve tubes; a second type of parenchyma with rounded ends forming 
loose tissue between sieve-tube groups. 
Mature growing, mature root. Showed no different features. 
Five-year stem. Sieve tubes small but with single transverse plate; pores in plate 
frequently few. 
One- to two-year stem. Sieve tubes of type 3, the same as in mature; very rare. 
Parenchyma of elongate cambiform type. 
Rhus typhina 
Mature. Phloem tissue uniformly thin-walled; sieve tubes abundant, with 1-5 
sieve plates upon an oblique end wall; frequently only a single plate; lattice 
not well developed. 
Companion cells abundant in corners of tubes. 
Parenchyma of conducting type, very thin-walled; cells about the same size as 
the sieve tubes. 
Three-year stem. Sieve tubes abundant but forming smaller proportion of phloem 
than in the mature; end walls either transverse or oblique with one plate or 
several; sieve plates rarely on side walls of tubes; lattice not seen. 
Parenchyma the same as in mature. 
Three-year root. The same as stem except for the presence of more storage tissue 
filled with starch. 
One-year stem, one-year root. Essentially the same as in three-year material; fewer 
sieve tubes in proportion to parenchyma. 
Acer saccharum 
Mature. Sieve tubes with a single transverse sieve plate in the majority of cases, 
frequently with 2-3 plates; lattice weak, a faint network of cellulose thick- 
enings upon the side wall; pores of lattice distinct under the oil immersion 
objective. 
Companion cells not readily distinguished because of condition of material. 
Parenchyma of divided-cambiform type in irregular tangential bands. 
Tilia americana 
Mature (fig. 39). Sieve tubes of type 2 with 2-10 sieve plates; rarely a single trans- 
verse plate; lattice well developed, much as in Populus. 
Companion cells abundant in corners of sieve tubes. 
