88 Mr. B. Clarke on Relative Position ; 



foregoing, i. e. either from the peculiar form of the ovary or by 

 the spontaneous growth of the ovule ; and in the case of Limno- 

 charis it appears rather to arise from the latter, as the ovary 

 makes no pressure on the greater part of the ovules. The posi- 

 tion of the raphe in the seed of Geranium Robertianum is how- 

 ever rather produced by pressure, as it is forced to become 

 ascending in consequence of being attached near the base of the 

 cavity, and in Nolana the external side of the ovule (on which 

 the raphe is situated) curves forward, giving it somewhat the 

 appearance of having been forced upwards in its growth. 



Value as a Differential Character. 



Should further observation show the position of the raphe 

 when differing fi'om its ordinary relation to the placenta to be a 

 character without exception in the families in which it occurs, it 

 will form an important distinction between many of them which 

 otherwise nearly approach each other ; thus Lauracese and Daph- 

 nacese have usually been considered as almost conterminous, and 

 the Urtical Orders have by most botanists been compared with 

 Chenopodiaceaj and its allies. It may also tend to a more defi- 

 nite distribution of the Orders in Alliances, as for instance of 

 those related to Rutaceae, Sapindacese, Rhamnaccse, and Clu- 

 siacese, as showing Erythroxylon to differ from Malpighiacese, 

 Spondias from Aurantiacese, &c. 



Berberis differs from Ranunculacese in having the raphe away 

 from the placenta, and Hedera from Camus in its being next the 

 placenta as in Umbelliferse. 



It may also show a distinction between Nolana and Convol- 

 vulacese, and its near approach to Boraginese, as the short raphe 

 in the latter family is next the placenta. 



The raphe next the placenta also separates some minor fami- 

 lies from others in or with which they have been included, as 

 Selaginese from Myoporacese, Scleranthacese (the position of the 

 cotyledons being equivalent) from Illecebracese ; and differences 

 in this character between many others usually regarded as in 

 near affinity will be seen by the Tables. 



As to whether a single pendulous ovule having the raphe next 

 the placenta ever occurs among Endogens is not fully ascertained, 

 as in Tamus the ovule is longer than the raphe, which also in a 

 very early stage has more or less the appearance of being lateral ; 

 and in Dioscorea and Rajania, where the raphe is also next the 

 placenta, the seeds are winged. These may be compared with 

 Menispermum where the raphe is very short, so that the ovule 

 in having its foramen superior must have it next the placenta, or 

 if the raphe is wanting, have an equivalent character ; so that it 



