CLASS MONCECIA. 



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 tlie swellings that appear there. 



278. The genus Calla includes the elegant exotic, Calla 

 ethiopica^ or Egyptian 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 fructiflcation 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 jpalustris^ 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 



Fiir. 156. 



uncovered ; at c is a pistil mag- 

 nified, showing the style to be very short, and the stigma ob- 

 tuse ; at <^ is a stamen bearing two anthers. The wild-turnip 

 (Arum) is nearly allied to the Calla, and the type of the natural . 

 order Araceae^ having flowers on a spadix with a fleshy rhizo- 

 ma, or cormus, and large, sword-shaped, or arrow-shaped leaves. 

 The arrow-head {Sagittaria)^ of the xoaterplantain 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 {Cur 

 curhitacecB)\ this includes not only the proper Cucumis, or 

 cucumber, which is an exotic, but some native genera of similar 



Elants ; we find here the gourd, squash, watermelon, and pump- 

 in. 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. Callar— Different speciea.— Family Arace»— Arrow-bead.— 879. Order Monadelphiar— Cucuitt« 

 ber tribo. 



