448 



THE MYRTALES 



shows that the sporophylls are of three lengths, short, medium 

 and long, an arrangement called heterostyly. It can readily be 

 seen that the three different lengths of the styles correspond 

 exactly with the position of the anthers, consequently whatever 



Fig. 322. Lower form of the Myrtales, flower perigynous: A, flower of 

 Lyfhrum. B, flower in section — c, lobe of the tubular calyx, from the margin 

 of which arise the petals, p. This flower has the long form of style and the 

 short and medium form of stamens. C, flower with medium style and with 

 short and long stamens. D, flower with short style and with medium and 

 long stamens. 



part of the proboscis or body of the bee or butterfly in visiting 

 these flowers comes in contact with one of the sets of open 

 anthers, exactly the same region of their bodies will touch the 

 stigmas as soon as they visit another flower with a corresponding 

 length of style. The spores from the three lengths of stamens 

 differ in size and color, and it has been demonstrated that better 

 results follow when crossing is effected between sporophylls of 

 the same length, i. e., long with long, short with short, etc. 

 Heterostyly arose in many of the orders, as among some of the 

 knotweeds, buttercups and rose families and in the gentians, 

 primroses, forget-me-not, etc. 



A higher and more characteristic type of the order is seen in 

 the Oenothera and in the great willow-herb {Chamaenerion, Fig. 



