CLASS M0N(EC1A. 
185 
and wood ; hence it will be seen, that if any foreign substance 
encircles the trunk it must in time produce a protuberance. 
The cambium from which the new layers are formed is inter- 
rupted in descending, and accumulates just above the inter- 
posing body, forming the swellings that appear there. 
278! The genus Calla includes the elegant exotic, Calla 
etMoploa, or ^gy^tian lily. The flowers having neither calyx 
nor corolla, grow upon a spadix ; the staminate and pistillate 
flowers are intermixed, the anthers are sessile ; the berries are 
one-celled, many-seeded, and crowned with a short style. This 
spadix thus covered with the fructification stands erect, sur- 
rounded by a spreading, ovate 
spatha; this, in the Egyptian 
lily, is of pure white, presenting 
a Very showy appearance and 
might be taken for the corolla. 
The Calla palustris, a very 
common American plant, is rep- 
resented at Fig. 156 ; at is the 
spatha, which is ovate, cuspidate, 
and spreading ; at 5 is the spa- 
dix covered with the fructifica- 
tion, the staminate and pistillate 
flowers being intermixed and 
uncovered ; at c is a pistil mag- 
nified, showing the style to be very short, and the stigma ob- 
tuse ; at 6? is a stamen bearing two anthers. The wild-turnip 
(Arum) is nearly allied to the Calla, and the type of the natural 
order Aracece, having flowers on a spadix with a fleshy rhizo- 
ma, or cormus, and large, sword-shaped, or arrow-shaped leaves. 
The arrow-head iSagittaria), of the water^lantain tribe, is un- 
like most of the Monoecious plants in general appearance; it 
has three sepals and three white petals ; it is not unlike the 
spider-wort in the form of its flowers. Many species of this 
delicate-looking plant may be found in autumn in ditches and 
stagnant waters. 
279. Order Monadelphia, or that in which the filaments are 
united in a column, presents us with the Cucumber tribe {Cv^ 
curhitacecB) this includes not only the proper Cucumis, or 
cucumber, which is an exotic, but some native genera of similar 
plants ; we find here the gourd, squash, watermelon, and pump- 
kin. These plants have mostly a yellow five-cleft corolla; calyx 
five-parted, three filaments united into a tube ; a large berry- 
like fruit, called a pepo ; this in the melon is ribbed, and in the 
278. Ca.lar-DIiferent species, — J'ainily Araceie — Arrow-bead. — 279. Order Monadelphia — Cacaia 
ber tiibe. 
