b 



228 MORPHOLOGY OF ANGIOSPBEMS 



yledona is to advance from naked flowers with parts spirally 

 arranged and indefinite in number to pentaeyclic trimerous 

 flowers. There are also such lines of advance as from apocarpy 

 to syncarpy, from hypogyny to epigyny, from actinomoiqjhy 

 to zygomorphy, etc. These tendencies are often very unequally 

 exjuessed even by different groups of the same alliance, one 

 group developing chiefly along one line, and another group 

 along another line, so that the results are very different. It is 

 also often a question whether a simple floral structure is primi- 

 tive or reduced. In the older morphology there was a typical 

 floral structure, and all simpler ones were regarded as reduced 

 forms. There can be no doubt that there are reduced floral 

 structures, as in Lemna ; but the great majority of simple 

 flowers are probably primitive. 



Upon these and other considerations, Engler has subdivided 

 the Monocotyledons into ten great alliances. The first six con- 

 stitute the more primitive Spiral series, and although the trim- 

 erous habit appears among them, the spiral arrangement and 

 indefinite numbers occur in one or more sets. The remaining 

 four alliances constitute the Cyclic series, the highly specialized 

 Monocotyledons. 



I. Pandanales. — This includes the Pandanaceae, Typha- 

 ceae, and Sparganiaceae, together containing a little more than 

 100 species. The Pandanaceae (about SO species), or screw- 

 pines, belong to the oriental tropics, chiefly the coasts and is- 

 lands of the Indian and Pacific oceans ; while the other families 

 are mainly represented in temperate regions. 



That these forms are primitive Monocotyledons is indicated 

 by the following facts: there is nothing to represent a perianth 

 unless the floral bracts of Sparganium be regarded as one; the 

 sporophylls are mostly spiral and indefinite in number, the sta- 

 mens of Pandanaceae often being very numerous and exhibiting 

 the greatest variation in arrangement ; the species are all hydro- 

 phytic; and the plants are anemophilous. Such flowers as those 

 of the Pandanaceae and Typhaceae are extremely simple, the 

 peculiar hairs accompanying the sporophylls of the latter ap- 

 parently representing sterile sporophylls; while the Spargania- 

 ceae are the most advanced members of the alliance, a perianth 

 probably being represented by a set of small bracts, and the 

 trimerous character appearing. 



