286 Dh. Thomson's Letters from Thibet. 



place in the system without calling it a distinct order. This, however, 

 is a mero dispute about words ; it is of no consequence whether it be 

 called a genus or an order, provided it be kept distinct from every other 

 order whatever; and if the place of such genera alongside of other 

 orders be not very clear, it may be prudent to collect them all together 

 at the end of the system, and arrange them according to some artificial 

 key. The objection to the last plan is, that if one's herbarium is arranged 

 according to some book, there will be a great number of genera placed at 

 the end, and thus widely removed from orders with which there is some 

 generally acknowledged affinity, though not a very intimate one. By the 

 former method, we have, in Endlicher's Genera Plantarum, genera intro- 

 duced at the close of those orders to which they are most allied, with 

 asterisks, to denote that these are only allied, but do not actually belong 

 to the order or agree with its character. But from the names and 

 characters of these genera not being printed in the same type as the 

 names of the orders, a person consulting the book will readily pass them 

 over, and not compare the plant in his hand with them. It appears to 

 me that both methods might advantageously be followed : the isolated 

 genera might be placed in the general system wherever the writer con- 

 ceives it to be best, with remarks upon them ; but all such ought again 

 to be arranged at the end according to some simple but accurate method, 

 to serve as a key to those which may be said to be 



Rari n antes in gurgite vasto. 



I have been led into these observations by having occasion lately to 

 consider the limits of the Order Polygalacese. 

 ** *** ***# 



I might illustrate these principles by a reference to many other orders, 

 but the above will suffice to show the necessity of as accurate and precise 

 definitions being given to natural orders, if we wish others to understand 

 our writings, or obtemperate to our views of affinity, as they are to genera; 

 and that it is necessary to reject a genus, if it breaks in upon a group 

 of genera already united by several prominent characters. It does not 

 matter much what becomes of the intruder : it must seek some other 

 house of refuge, or occupy one by itself, if it cannot procure entrance into 

 another, or get some friend to associate with it, without a quarrel. 



Letters were read from Dr. Thomas Thomson, jun., dated Iskardo, 

 the most northerly part of the Indus, from which it appeared that 

 the first division of the Thibet expedition under his charge would be 

 detained at this station during the winter, in consequence of the depth 

 of snow in the mountain passes into Cashmere, which is the next destina- 

 tion of the expedition. The appearance of the country at this season was 

 described as rather desolate. The valley of the river is filled with 

 alluvial deposits, sometimes containing shells (planorbis and lymnaea 

 were found). The height above the sea of Iskardo is 7000 feet. The 



