DEVELOPMENT OF PLANTS 443 



of showy flowers and the large tubular corollas which attain their 

 highest perfection in several of the families. 



(a) The More Important Families of the Phlox Order. The 

 flowers of the lower families are regular, as in the morning- 

 glory, sweet potato, dodder (Cuscuta) , a yellow thread-like para- 

 site that twines about various plants, and the phlox (Fig. 329). 

 The flowers of the rough-leaved borages (Boraginaceae) are 

 also regular but they are distinguished by having the ovary of 

 the two carpels deeply lobed so that the fruit appears as four 

 nutlets and also by their coiled inflorescences as shown in Fig. 

 330. This family includes the heliotrope, hound's-tongue (Cyno- 

 glossum), forget-me-not (Myosotis), comfrey (Symphytum) , 

 and the blueweed (Echium) in which the corolla becomes 

 irregular. 



The mint family, Labiatae, is world-wide in its distribution 

 and the largest of the order with 3,000 species. These plants 

 are sharply characterized by square stems, opposite leaves, aro- 

 matic oils, nut-like fruits as in the borages, but the corolla is 

 very irregular and usually two-lipped. The stamens, usually 

 two short and two long ones, together with the two-lobed style 

 are more frequently concealed under the upper lip of the corolla 

 (Fig. 331). The flowers are generally so placed that the lower 

 lip serves as a landing place for insects and in entering the 

 flower, the top of their bodies rubs against the stigmas or anthers. 

 Crossing is secured by the difference in the time of the matura- 

 tion of the anthers and stigmas, assisted by a variety of move- 

 ments, such as the alternate curving down of the anthers and 

 stigmas which brings first one set of organs and then another 

 into the pathway of the insect. One form of this arrangement 

 is seen in the sage, where there are but two strangely modified 

 stamens, the two anther lobes being connected by a long-curved 

 rod which is fastened near one end to a short filament so that 

 the anther becomes a lever with the filament as a fulcrum (Fig. 

 332). Only the anther lobes concealed under the upper lip are 

 fertile. As the bee enters the flower, he pushes up the short 

 arm of the lever, thus causing the long arm to swing down, 

 pressing the fertile anther upon his back and dusting him with 



