214 PRACTICAL COURSE IN BOTANY 



IV. SPECIALIZED FLOWERS 



Material. — For spring and early summer: sweet pea, black locust, 

 wistaria, lui)ine, or any of the characteristic butterfiy-shaped Huwers of 

 the pea family. For autmnn or late smnmer : tropa?olmn, monkshood, 

 or a bilabiate flower — snapdragon, digitalis, dead nettle, salvia, catalpa, 

 etc. — of the mint or figwort family. 



237. Irregularity and specialization. — Irregularity and 



bilateral regularity are, as a rule, indicative of specialization, 

 or adaptation to a particular purpose, such as the ready 

 distribution of pollen, or its protection against injury. These 

 adaptations are more noticeable in the corolla than in other 

 parts, and hence flowers of this kind are usually classed 

 according to the shape of their corollas. The most highly 

 specialized flowers in this respect are the orchids, but they 

 are too rare and difficult of access to be available objects for 

 study. The most familiar and widely distributed kinds of 

 speciahzed corollas are the bilabiate, or two-lipped, and the 

 papilionaceous, or butterfly, forms. The first is characteris- 

 tic of the mint and figwort families, of which the toadflax, 

 sage, and catalpa are familiar examples. The second com- 

 prises the well-known papilionaceous flowers of the pea 

 family, named from the Latin word papilio, a butterfly, on 

 account of their general resemblance to that insect. 



238. Dissection of a papilionaceous flower. — Sketch a 

 blossom of any kind of pea or vetch as it appears on the 

 outside. Are the sepals all of the same length and 

 shape? If not, which are the shorter, the upper or the 

 lower ones? 



Turn the flower over and examine its inner face. Notice 

 the large, round, and usually upright petal at the back, the 

 two smaller ones on each side, and the boat-shaped body 

 between them, formed of two small petals more or less united 

 at the apex. Press the side petals gently down with the 

 thumb and forefinger and notice how the essential organs are 

 forced out from the little boat in which they are concealed. 



