LACTUCA SATIVA 



615 



heads i or z feet in height. In the asparagus type, the lanceolate 

 leaves are 6 to li inches in length, i or x inches in width, usually 

 entire but sometimes lobed. 



The Inflorescence and Flower. — The floral axes reach a 

 height of 2. to 4 feet or more and form a branched, bushy crown. 

 The branches bear leaves that are commonly sagittate and clasping 

 and are terminated by the inflorescences. The inflorescence con- 

 sists of a cymose cluster of heads each of which contains from 15 

 to X5 or more flowers, al- 

 though fewer may occur 

 in some instances. The 

 oldest head of the in- 

 florescence is the terminal 

 one, and the lateral heads 

 are axillary. (Fig. 3x5, 

 A.') The ligulate flowers 

 are all perfect and alike. 

 The flower primordia arise 

 simultaneously from a 

 naked receptacle which is 

 at first conical, then con- 

 vex, and finally flat and 

 broad. (Fig. 316, y4.) As 

 the individual primordium 

 enlarges, a marginal ring 

 forms, which marks the 

 initiation of the corolla 

 tube. (Fig. 316, B.) This 

 elongates and a fold of 

 meristematic tissue arises 

 at the base of its adaxial 

 surface from which the staminal rmg develops. At the same time, 

 a ring of tissue is formed outside and at the base of the corolla tube 

 which gives rise to the pappus. (Fig. 32.6, C, D.) The carpellary 

 primordia are the last to appear; and, by the time they begin to 

 differentiate, the corolla has started to incurve over the tip of the 

 floral axis. (Fig. 3x6, D, £.) The single cavity of the ovary is 

 formed by the upward growth of the carpellary tissue. The 

 growth of the undi verged tissue of the carpels, corolla tube, and 

 calyx tube results in the elevation of the anthers, the strap of the 



Fig. 315. A, habit of flower; B, unopened head; 

 C, longisection through head ; D, single flower ; 

 E, flower with corolla removed ; F, akene with 

 pappus ; G, floral diagram. 



