68 APETALOUS FLOWERS [CH. 



Truly achlamydeous flowers are much rarer than mono- 

 Mamydeous flowers, however. In these latter either the 

 calyx or the corolla is wanting, and far more commonly 

 the corolla. Examples are found in Clematis, Mezereon, in 

 the common Elm, Nettle, &c., and in the Natural Orders 

 Caryophyllacese, Chenopodiacea3 and Polygonacea3, &c. 



Owing to technical difficulties in determining by direct 

 observation in the field whether a flower is rnonochlamy- 

 deous or achlamydeous e.g. Oak, Beech, Alder, Birch, 

 Willow, &c. it is customary in floras to deal summarily 

 with such flowers and term them generally apetalous, 

 since, when monochlamydeous, it is the calyx which 

 usually occurs. 



Good illustrations of more or less difficult cases are 

 the following. 



In the common Arum an inflorescence (Spadix) of 

 truly achlamydeous flowers is subtended by one large 

 protective bract (Spathe). 



In the Willows we have an inflorescence (Catkin) 

 consisting of numerous bracts, in the axil of each of 

 which is an achlamydeous flower. The whole catkin is 

 distinguished from a flower by the axillary structures 

 if the bracts were sepals we should not find stamens or 

 ovaries in their axils. 



In like manner the axillary position of the achlamy- 

 deous or monochlamydeous flowers of the Birch, Alder, 

 Poplar, Beech, Oak, &c., guides us to their true nature ; 

 and similarly with the apetalous flowers of Grasses, 

 Sedges, &c. 



Another point arises when, as in Lilies, Hyacinths, 

 Daffodils, &c., the sepals and petals are all alike : close 

 examination of a Lily shows that the three sepals are 

 inserted outside and alternate with the three petals, but 

 they are all so similar in shape, colour, texture and other 



