254 MONOCOTYLEDONS. 



bling a seal. The onion, smilax, asparagus, lily of the valley, 

 etc., are members of the lily family. The parts of the flower 

 are usually in threes, though there is an exception in the genus 

 Unifolium, where the parts are in twos. A remarkable excep- 

 tion occurs sometimes in Trillium grandiflorum, where the flower 

 is abnormal and the parts are in twos. 



493. Floral formula. — A formula is sometimes written to show at a glance 

 the general points of agreement in the flower among the members of a 

 family or group. The floral formula of the lily family is written as follows : 

 Calyx 3, Corolla 3, Androecium 6(3-3), Gyncecium 3. The formula may be 

 abbreviated thus : Ca3,Co3,A6(3-3),G3. 



493. Adhesion and cohesion. — In the lily family all the sets, or whorls of 

 parts, are free ; that is, no floral set is adherent to another. Farther, the 

 parts of the calyx, corolla, and andrcEcium are distinct. But the parts of the 

 gyncecium are coherent, i.e. the three carpels are united into a single com- 

 pound pistil. In the floral formula this cohesion of the parts of a set is 

 represented by a small bracket over the figure, as in the gyncecium of the 

 lily family. 



494. Floral diagram. — The relation of the parts of the flower on the axis 

 is often represented by a diagram, as shown in tig. 326 for the water-plantain 

 family. 



495. Note. — In the following lessons on plant families practical exercises 

 may be conducted, employing representative plants in the several important 



families. Sketches should be made of the form of the 

 leaves, their relation to the stem ; stipules ; parts of 

 the flower, and other salient and important characters. 

 Floral formulas and diagrams may be made. Brief 

 notes and descriptions, made from the specimens them- 

 selves and not from the books, should be appended. 

 The plants chosen here need not be insisted upon, for 

 Fig. 326. others equally good may be found. The studies 



Diagram of alisma presented are offered as suggestions to indicate the 

 flower. (Vines.) ^* 



way m which relationships may be detected, and a 

 familiarity with the characters of the families may be obtained. Several of 

 these lessons are chosen among the monocotyledons, t(. which the lily family 

 also belongs. 



496. Water-plantain family (alismacese). — If we wish to begin with a 

 more simple and primitive family, the water-plantain family will serve the 

 purpose. The common water plantain (Alisma plantago) is an example. It 

 occurs in ditches and muddy shores of streams and lakes. The flowers are 

 in a loose panicle and are inconspicuous. The leaves resemble those of the 



