DEVELOPMENT OF PLANTS 471 



tinguished from other orders. More frequently they consist of 

 five regular whorls of five members each, anthers usually opening 

 by pores and often provided with two horn-like appendages, and 

 the pistil is composed of five carpels, the ovary maturing as a 

 capsule or berry (Fig. 326). The separate origin of each whorl of 

 organs is an important feature of the order as contrasted with 

 other Sympetalae, each set being as a rule separately attached to 

 the receptacle. While the sympetalous corolla is a step in ad- 

 vance of previous types, it is evident that these regular hypogy- 

 nous flowers are in other respects of a rather simple character. 

 This feature is further illustrated in some of the genera like 

 Clethra, Monotropa and Pyrola where the free or slightly fused 

 petals form a very natural transition from the Choripetalae 

 (Figs. 327, A; 326). 



The simpler forms of flowers are illustrated in Pyrola with 

 its regular hypogynous and polypetalous flowers, though some 

 species show a slight tendency to sympetaly. The stigmas are 

 mature with the opening of the flower while the anthers are 

 bent back out of the way, their filaments being held under con- 

 siderable tension by the petals (Fig. 326, A, B). A bee laden 

 with spores would effect a crossing as soon as he alighted upon 

 the flower, but in probing after the nectar he presses back the 

 petals, thus releasing the anthers which snap down, spilling the 

 spores upon him. Doubtless autogamy results in many of these 

 forms if crossing fails owing to the expansion of the petals 

 which would release the stamens, and the drooping of the flower 

 which would bring the falling spores in line A^ith the stigma 

 (Fig. 326, C, D). 



Other genera show varying degrees of sympetaly but in the 

 majority of cases, tubular corollas appear (Fig. 327, C) as in the 

 Leucothoe, bearberry, Andromeda, blueberries, etc. The majority 

 of such forms have ' horned anthers which are shaken by the 

 insect and so assist in sifting out the spores. In the Blueberry 

 family, we note that a mass growth of the receptacle and ovary 

 has begun (Fig. 327, D) while in Rhodora, rhododendron and 

 azaleas another line of variation appears in the irregular corolla 

 (Fig. 327, r). In the two latter genera, the styles and stamens 



