136 



thickets along the river-banks. This list must be regarded 

 as an experiment. It is based on all the sources of infor- 

 mation which have been available to me. The most impor- 

 tant of these are: BUNGE'S Reliquiae Lehmannianae, Madame 

 FEDTSCHENKO'S and BORIS FEDTSCHENKO'S various works, 

 LIPSKY'S systematic memoirs in Acta Horti Petropolitani, 

 LITWINOW'S descriptions some in the schedules to Herbarium 

 florae Rossicae, others in "Travaux de la Musee de 1' Aca- 

 demic", and finally it is based on my own collections. 



Two great difficulties had to be contended with in com- 

 posing the list. First the records of occurrence in the various 

 memoirs are not always sufficiently exact to allow of an 

 accurate determination as to whether the plant in question 

 occurs on the territory dealt with in this work, or north of 

 our selected boundary, or on the mountains to the east or 

 south of it; secondly it is difficult to determine the limits of 

 any particular species in a flora which is still insufficiently 

 investigated. I have therefore adopted a somewhat broad 

 outlook as regards this question and have therefore excluded 

 several "minor species" described in recent years by WINKLER, 

 LITWINOW and others. The synonymy also presents difficul- 

 ties which, however, I hope have been surmounted in most 

 cases. 



I am fully aware that the list as such has many defic- 

 iencies, but hope that it may serve the purpose for which 

 it has been prepared, namely to give fairly accurate infor- 

 mation about the growth-forms of the desert. 



As regards the growth-forms I have chosen the system 

 proposed by RAUNKLER, partly because, in spite of its one- 

 sidedness, it emphasises one of the most important features 

 of plant-life, also because it is easier to handle than other 

 classifications of growth-forms, and finally because by using 

 RAUNKLER'S system it is possible to express statistical data 

 which may be compared with corresponding data for other 

 regions. 



The biological types (growth-forms) of RAUNKLER (see 

 Raunkiaer 1904, 1905, 1907) are arranged according to the 

 way in which plants live through unfavourable seasons, and 

 special emphasis is laid on the degree and kind of protection 



