626 



PHANEROGAMS. 



formed into petaloid staminodes. It has already been pointed out how the flowers 

 of Gramineae and Orchideae can be traced back to the trimerous pentacyclic type ; 

 the theoretical diagrams here given (Figs. 426 — 433) will answer the same purpose 

 for some of the other more important families. 



If the pentacyclic flower with the formula S^Pn^L^n^ni+n) is considered as 

 the typical one for Monocotyledons, it will be seen that the great majority of 

 families the number of whose parts deviates from this type do this only by 

 the suppression of single members or of whole whorls, the typical position of 

 those that still remain with respect to one another not being disturbed. The 



Fig. 431. — Diagram of Alisniacese ; A Bntomus, B Alisnia. 



FIG. 432.— Diagram of Triglochm (Juncagineae). 



variety in the forms of flowers in this class is therefore brought about almost 

 entirely by abortion ^ ; and it is not uncommon for abortion to be carried to such 

 an extent in Monocotyledons that nothing is left at last of the whole flower but 

 a single naked ovary or a single stamen, as happens frequently in Aroideae. In 

 these cases a similar explanation of the relationships of the parts of the flower is 

 rendered possible and even evident by the occurrence of flowers with the actual 

 typical structure, and by a complete series of transitions caused by partial abortion. 

 It is especially in small closely crowded flowers, as those of Spadiciflorae, Glumi- 

 florae, &c., that so great a reduction of the typical number of members is observed ; 



Fig. 433.— Diagram oi Cymiiostachys (Aroideje), after Payer. 



while in larger and more isolated flowers the number of members in each whorl 

 is usually complete or even excessive (as Butomus and Hydrocharis), and deviations 

 usually result from petals (or petaloid staminodes) being formed in the place of 

 fertile stamens (e.g. Scitamineae). With reference to the abortion which is often 

 carried to so great an extent in small flowers, it may in certain cases even be 

 doubtful whether in an assemblage of stamens and carpels we have a single flower 

 or an inflorescence consisting of several flowers reduced to a very simple state by 

 abortion, as for example in Lemna. 



* Compare what was said on Abortion at p. 222 and in the Introduction to Angiosperms. 



