348 Minnesota Plant Life. 



parts of the same area. The violet flower, with one of its petals 

 spurred, is conceived to be higher in rank than the linden flower, 

 in which all the petals are alike. Irregularity of the flower 

 marks some improvement over regularity, and it should always 

 be remembered that the irregular flower is irregular for a pur- 

 pose. The irregularity may be, and usually is, an adaptation 

 to the habits of the insects which eft'ect pollination. There- 

 fore, the strongly irregular flowers of orchids, beautifully 

 adapted to the sizes, shapes, weights and feeding-habits of bees 

 or moths, are improvements over the regular flowers of tulips, 

 blue flags and trilliums. Irregularity may arise in a variety 

 of ways. A very common type is two-sidedness of the flower and 

 the substitution of the two-sided symmetry for the radial sym- 

 metry. Just as man, whose body can be divided into approxi- 

 mately equal halves by only one plane, is on this account a 

 higher structural type than the starfish, the body of which may 

 be divided into several approximately equal portions by planes 

 radially disposed, so the two-sided flower of an orchid, or that 

 of the pea or larkspur, must be regarded as structurally higher 

 than related radially-symmetrical forms, such as lilies, acacias, 

 lindens or buttercups. 



Along with the development of upper- and under-sidedness 

 in the flower go a number of changes in the shapes, positions, 

 numbers and sizes of the floral organs. Thus in the pea flower, 

 one petal is larger than the others, and forms the so-called 

 standard. The other four petals, grouped in pairs, constitute 

 the so-called wings and keel of the flower. The stamens are 

 blended together into a tube, but one stamen in the plane of 

 symmetry stands distinct from the rest. The carpels, too, in 

 the pea flower become reduced in number and the i)od is often 

 flattened in the plane of the symmetry. 



There should be no difliculty in comprehending how a flower 

 that manifests in its whole structure a great departure from 

 the primitive type should be considered as higher than a flower 

 that approximates in its structure more closely to the early 

 conditions. It must be observed, moreover, that the dift'erent 

 orders of flowering plants do not constitute a single series of 

 advancement. (Jne order may show improvement along one 

 path, while another shows improvement in (|uite a difl'erent 



