642 



PHANEROGAMS. 



flower is tetramerous or pentamerous the number of carpels is usually less ; when the 

 flower is dimerous or trimerous, or when the parts are arranged spirally, the number 

 of carpels is not unfrequently larger. 



It will be seen from this brief outline that the relations of number and position 

 in the parts of the flowers of Dicotyledons are very various, and cannot be referred, 

 as is the case with Monocotyledons with but few exceptions, to a single type. Even 

 the establishment of diff"erent types for the larger groups is attended with great 

 uncertainty, since the knowledge of development necessary in order to refer par- 

 ticular forms of flowers to general formulae is often wanting. The too universal 

 application of the spiral theory of phyllotaxis in the case of cyclic flowers has 

 often increased the difficulty, and has even occasioned doubts which would not 

 have arisen without the theory. 



For the great majority of Dicotyledons the floral formula may be given 

 '^n^n'^^n{+n+...)^n{-m)' This formula holds good for most pentamerous flowers 

 and for those which are truly tetramerous (or octamerous as Michauxia) ; so that n 

 is in these cases 5 or 4 (or 8 as the case may be). In the androecium an indefinite 

 number of (alternating) whorls -S'/„(+„^ ^ must be assumed in order to include 



Fig. 440.— Diagram of Caprifoliaceae; A Ley- 

 cesteria, a Lo?iicera, b Symphoricarpus . 



Fig. 441.— Diagram of Par- 

 nassia (Saxifragacese). 



Fig. 442. — Diagram of Campanulaceae ; 

 A Campanula, a Lobelia. 



the large number of flowers in which the androecium consists of more than one 

 whorl (as e.g. Fig. 451). The mode of expressing the gynaeceum C,j(_„j) is intended 

 to show that very commonly the number of carpels is fewer than 5 or 4 (or 8 as the 

 case may be) ; m may be of any value from o to n. In the majority of gamopetalous 

 orders and elsewhere there are very commonly only two carpels ; and in this case 

 they stand in a median line posterior and anterior ; but on the hypothesis that the 

 typical gynaeceum consists of five alternating carpels and has been reduced to two by 

 abortion, one must stand in the median position in front, the other obliquely behind. 

 A similar difficulty is also presented when the gynaeceum consists of three or of 

 only one carpel. It would carry us too far to detail the reasons which nevertheless 

 determine me to retain the formula above given for the gynaeceum of flowers of this 

 description ; it need only be mentioned that species or genera with the typical five 

 carpels occur in the most diverse families and orders where a smaller number is the 

 normal one. 



The diagrams Figs. 440-450 represent a selection of cases which can be 

 reduced (if no further reference is made to the consideration mentioned above) to 

 the general formula which here assumes the simpler expression -S",, P^^ St^ C'h(_,„). 



