BH Dr. Arnott on the tntroductbn *f 



(Dr. Walker Arnott,) in the article Botany in the Encyclopaedia Britan- 

 nil ;i, by which it would be a mere modification of a common axile placen- 

 tation. Dr. Lindley was the first to indicate that the placentation was 

 parietal: but that view was weakened by Dr. Wight, (in his Illustrations 

 of Indian Botany, and in the Madras Journal,) who reverted to the axile 

 utation, but apparently differing from Seringe, by supposing that it 

 was the upper surface of the carpellary leaf that was next the axis. He 

 then referred to the opinion stated by Dr. Lindley in the " Vegetable 

 Kingdom," that the true structure of the Cucurbitaceae had been mis- 

 apprehended, " the illusion having arisen from three parietal placentae, 

 with revolute (convolute is obviously meant) seed-bearing edges projecting 

 forward in the cavity where they adhere." Dr. Walker Arnott mentioned 

 that he had come to "a different conclusion from all these by observations 

 made during last autumn, at a time when he had no opportunity of con- 

 sulting any works on the subject. He agreed with Lindley that the pla- 

 centation is truly parietal, but differed with him widely as to what were 

 the carpellary leaves, the true ones being revolute, not convolute, and 

 alternating with those considered as such by Lindley; in fact they are 

 represented by the dark places in Lindley 's figure, (p. 313.) This theory 

 agrees most with Dr. Wight's, and chiefly differs in this, that the carpel- 

 lary leaves are at first distinct from each other, and not united till the 

 ovary is advanced, which latter hypothesis is necessary to the axile 

 placentation. 



March 14, 1848. — Mr. Gourlie exhibited specimens of Gutta Percha, 

 and read an account of that substance by Dr. Oxley of Singapore, pub- 

 lished in the Journal of the Indian Archipelago. He also exhibited a 

 specimen of Strychnos toxifera (Sir K. Schomburgh). 



April 18, 1848. — The following paper was read: — 



XLIH. — On the Introduction of Anomalous Genera into Natural Orders. 

 By Gr. A. Walker Arnott, LL.D., Regius Professor of Botany. 



In defining natural orders, or in referring plants to them, it appears to 

 me, that of late years botanists have been frequently pursuing a method 

 which must soon lead to inextricable confusion. When one reads the 

 character of an order, it is to be expected that every plant referred to 

 it must not positively disagree with that character. The character of 

 a species ought to be such, that any of its varieties will arrange themselves 

 under it : — in the same way in a genus we have a right to expect that 

 no species will be referred to it that militates against the generic 

 character. The character may be altered according as we know new 

 species, or if we see occasion to break up the old genus into several; 

 but there must be no incongruity between the generic character and 

 the plants referred to the genus. And, indeed, it is rare we find this 

 to be the case, unless when through laziness one has taken the generic 

 character without sufficient examination from some book, and admits 



