205 



one of the lateral carpella and the displacement of the other so as to 

 become opposed to the persistent posterior carpellum ; in Agrimonia 

 and Spiraea (when dicarpous), from a similar suppression ; as also in 

 reduced fniils of Reseda kiteola, &,c. ; 3rdly, oblique, which he de- 

 scribes as of frequent occurrence both in plants in which the carpella 

 are generally anterior and posterior, and in those in which they are as 

 predominantly right and left, and which he supposes to arise from the 

 remaining lateral carpellum of a tricarpous ovary retaining nearly its 

 original position when the other lateral carpellum has disappeared, in 

 consequence of w'hich the posterior carpellum is somewhat displaced, 

 becoming obliquely posterior. He regards the single carpellum as 

 the result of the non-development of one of the carpella of a dicarpous 

 ovarium, and its position may consequently vary in three different 

 ways: 1st, anterior, as occurs in 1-carpellary ovaries of Myrtaceae, 

 Onagrarise, Polygaleoe, Leguminosae and Acanthaceae, to which may 

 probably be added Hippurideae, Bruniacege, &c ; ^wdXy, posterior, as 

 in the 1 -carpellary ovaries of Houttuynia cordata and Piperaceae ; 

 3rdly, lateral or oblique, instances of which occur in Morese, in Ela- 

 tostemma, and in Celtidese. The normal number of carpella in all 

 ovaries he regards as three or a multiple of three; the additional series 

 being frequently reduced by abortion in the same manner as the first, 

 and thus giving rise to the formation of ovaries with four and five car- 

 pella. Tricarpous ovaries generally have their component parts 

 placed two laterally and one posteriorly; but exceptions to this rule 

 occur, as for example in Viola, where the third carpellum is anterior, 

 and in Clethra, Piltosporum and Delphinium, in which the position 

 of the carpella varies in the same plant. 



Mr. Clarke next proceeds to consider the value of the characters 

 derived from the position of the carpella, for which purpose he has 

 framed a large table containing the results of long-continued observa- 

 tions on a multitude of exogenous plants with monocarpous or dicar- 

 pous ovaries. In this table he constitutes two primary divisions, viz., 

 Proterocarpous, in which the carpella when single are anterior or 

 lateral, never posterior; and Heterocarpous, in which the single car- 

 pellum is for the most part a mixture of lateral, anterior and posterior, 

 and is rarely wholly posterior. The position of the component parts 

 of the dicarpous ovarium also appears to be more permanent in the 

 first than in the second division. From this table Mr. Clarke deduces 

 various inferences in relation to the systematic arrangement of plants, 

 and the importance of the characters derived from the position of the 

 carpella, and more especially from that of the single carpellum, which 



