HISTOLOGY OF PHLOEM IN WOODY ANGIOSPERMS 
355 
Four-year stem (fig. 14). Sieve tubes small, 6-18 n; few in proportion to parenchyma 
cells; lattice not well developed. 
Companion cells rare, about as abundant as in mature. 
Parenchyma of divided cambiform type; some cells longer than others. 
Four-year root. Same as the four-year stem except more storage tissue; sieve tubes 
in groups separated by wide rays. 
Two-year stem (fig. 13). Shows further reduction in size and number of sieve tubes 
and increase in proportional amount of parenchyma. 
Two-year root. Same as the two-year stem except for increased amount of storage 
tissue. 
Juglans cinerea 
Mature, growing and mature root same as Juglans nigra except that latter has more 
fibers in phloem. 
One-year stem (fig. 12). Sieve tubes very small and scarce; sieve plates 8-12 fx in 
width; lattice not apparent; oblique end wall with several plates with 
poorly developed pores; companion cells not found but probably present; 
parenchyma abundant, some cells elongated and conspicuously pitted, others 
short and packed with starch. 
Carya cordiformis 
Mature (fig. 9). Sieve tubes single or in groups of 3 or 4 surrounded by single row of 
parenchyma cells, each strand of sieve tubes and parenchyma embedded in 
an almost solid mass of fibers; sieve tubes with very oblique end wall, with 
10 to 20 sieve plates (fig. 9) ; lattice very regular, cross-bars separating sieve 
fields; pores of sieve fields very minute, pores in sieve plates on end walls 
3-4.5 ^^ in diameter. 
Companion cells present in corners of sieve tubes, difficult to determine 
Parenchyma of divided cambiform type, abundantly pitted on radial walls, 
confined to sieve tubes or in narrow tangential bands; many cells filled with 
tannin. 
Carya ovata 
One-year stem, one-year root. Same as above-described species in essential features; 
sieve tubes small; 3 to 4 sieve plates on oblique end walls, plates rather widely 
separated; lattice very faint. 
Companion cells probably present. 
Parenchyma heavily pitted and abundant. 
Fagus grandifolia 
Mature. Sieve tubes large with single transverse sieve plates 50-60 ix across; pores 
on sieve plates large, 6-9 fx in diameter, pores on lattice distinct but small, 
about 0.5 jLt; lattice not well developed. 
Companion cells not easily seen on account of condition of material. 
Parenchyma scattered, not abundant. 
Castanea dentata 
Mature. Sieve tubes in rather small numbers as compared with parenchyma; end 
walls oblique with 4-8 large sieve plates; lattice about as in Populus. 
