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as one of the most isolated. It is allied to Sphaerophysa 
which likewise belongs to the interior of Asia, and to Colutea 
which is distributed from the south of Europe to the western 
Himalaya. 
Holopleura, so far as I can learn, is insufficiently known 
and there may be some doubt as regards its right to generic 
rank. REGEL says that it is related to Carum and Rumia. 
Miltianthus is related to Zygophyllum. 
Among the endemic species scarcely any one stands 
isolated. Whichever one be named, it is possible to indicate 
closely related species in the surrounding countries, more 
especially those towards the South and South-west. Through 
more intensive systematic studies one could probably enumerate 
a series of pairs of vicarious species. Studies of this kind 
have not been undertaken here, as I have restricted myself 
to the investigation of the distribution of the genera which 
contain endemic species in the lowlands of Transcaspia. The 
following genera have their main distribution in the Medi- 
terranean countries, especially in the eastern ones, and in 
Nearer Asia whence some of them extend right into Central 
Asia. 
Heliotropium Pterotheca Allium 
Lappula Scorzonera Limodorum 
Rochelia Convolvulus Cistanche 
Gypsophila Isatis Hypecoum 
Herniaria Malcolmia Trigonella 
Saponaria Peltaria Crucianella 
Silene Sisymbrium Haplophyllum 
Centaurea Crypsis Scrophularia 
Echinops Lepturus Tamarix 
Jurinea Lagochilus Cachrys 
Rhaponticum Phlomis Ferula 
Matricaria Tulipa Valerianella 
The following genera seem to have their main distri- 
bution more to the East, in the interior of Nearer Asia and 
in Central Asia: 
