I 
480 Saunders .— A Reversionary Character 
Concerning the Cruciferae. 
16. The typical gynoecium is composed of four carpels, of which two 
form sterile valves, the other two which have become solid remaining fertile. 
In some few genera this relation is reversed. The solid members usually 
develop centripetally until they meet, and so form a complete partition 
(the replum), but in other cases the inward growth is arrested at an early 
stage, so that the partition is wanting or remains incomplete. Thus, the 
anomaly that from the first moment of their origin the placentae should be 
as large as, or even larger than, the carpels to which they belong disappears 
now that these placentae are shown to be independent carpels. 
17. Outgrowths from the upper extremities of the carpels, such as are 
seen in Matthiola bicornis , DC., M. tricuspidata , R. Br., and Parolinia 
ornata , Webb, become intelligible when the tetramerous structure of the 
gynoecium and the division of labour among the two pairs of carpels is 
realized. 
18. Ovaries of more than four carpels generally show a number of 
furrows, ridges, ribs, wings, or prominent parallel veins corresponding with 
the number of the solid or of the valve carpels present. Thus, e. g. in the 
genus Isatis the contour of the fruit in one species indicates the presence of 
six valves, in another of ten. From the character of the veining the number 
of carpels in species of Brassica and Sinapis appears to be sixteen ; from the 
number of wings, sixteen in Guiraoa arvensis , Coss.; from the ribbing, between 
forty and fifty in species of Rapistrum. It is necessary, however, to dis¬ 
tinguish between formations associated with parallel veining and other out¬ 
growths produced as the result of the presence of strong lateral veins, such 
as the horns in Tetracme , which are not significant of the carpel number. 
19. The presence of this large number of carpels in various lomentose 
fruits accounts for the formation of the subsidiary loculi at the joints 
between the seed-containing sections. 
20. The stigmatic function is usually restricted to the solid carpels, 
but it may be subserved by the valve carpels ( Matthiola incana) or by both 
(probably the case in Biscutella). 
21. The evolution of the solid carpel is to be seen in progress in certain 
types which produce characteristic dimorphic fruits, as e. g. Aethionema 
heterocarpum , J. Gay, and Diptychocarpus strictus , Trautv. 
22. Many types produce a few reversionary multicarpellary fruits, 
generally, however, only at the beginning of the season and under favourable 
conditions (observed in some twenty genera). 
23. Rarely this reversionary condition may be exhibited throughout 
the greater part of the plant, as in Tetrapoma {Nasturtium) palustre , 
Holargidium {Draba)> and to a less extent in Lepidium sativum , L. In 
these cases the character is not inherited in the strict sense, but it may 
