356 
L. H. MACDANIELS 
Companion cells rare. 
Parenchyma of two types, one with protoplasmic contents, sometimes tannin, 
the other brick-shaped, apparently empty, with conspicuous sieve-like pitting 
on all walls especially the radial and terminal, (This type distinct and 
unusual.) 
Ulmus americana 
Mature (figs. i6, 17). Sieve tubes collapsed except close to cambium; sieve plates 
transverse with large meshes, 4-7 /x in diameter; lattice with prominent cross- 
bars and conspicuous pores (fig. 17); pores of lattice about 0,6-0,8 in 
diameter. 
Companion cells frequent. 
Parenchyma of two types: one large and tannin-filled, arranged in tangential 
rows; the other divided-cambiform, heavily pitted on radial walls, scattered 
among the sieve tubes, 
Growifig. No new features except reduction in amount of sclerenchyma. 
Five- to six-year stem. Sieve tubes very small and scarce; of the same type as those 
of the mature stem; lattice not well developed. 
Parenchyma as in mature but a proportionally larger amount in relation to sieve 
tubes. 
Three-year root. Sieve tubes very rare, difhcult to find; sieve plates transverse as 
in mature, but poorly developed; sieve tubes of about the size of some of the 
parenchyma cells. 
Parenchyma abundant, thin-walled. 
Madura pomifera 
Mature (fig. 18), Sieve tubes short and broad with transverse sieve plates in tan- 
gential bands between bands of heavily pitted parenchyma; lattice not well 
developed. 
Companion cells fairly common. 
Parenchyma of two types; one heavily pitted on radial and transverse walls, 
the other thin-walled, containing crystals; these arranged in bands in the 
following succession: 4-5 rows of heavily pitted parenchyma, 1-2 rows of 
crystal-containing parenchyma, 2-4 rows of sieve tubes. 
Morus alba 
Mature (fig. 19). Sieve tubes abundant, short, rather wide, with a single transverse 
sieve plate; lattice forming a distinct network as in Ulmus; pores in lattice 
distinct. 
Companion cells in about one half of sieve tubes. 
Parenchyma of divided cambiform type, heavily pitted on radial wall; not filled 
with tannin; scattered among sieve tubes and in irregular tangential bands. 
Liriodendron Tulipifera 
Mature (fig. 21). Sieve tubes of type 2, with 6-10 sieve plates upon an oblique end 
wall; lattice of rounded, well-defined sieve areas on both tangential and 
