170 



In Transcaspia the conditions are just the reverse. As 

 may be seen from table 1 (p. 17), the precipitation is greatest 

 in winter so that the coldest season is comparatively humid. 

 In this respect the climate to a certain degree favours 

 the growth of trees. But as a whole it is only to a slight 

 degree favourable! The long dry period which occurs during 

 the vegetative period for trees necessitates the utmost economy 

 as regards water. Therefore only the more xerophytic trees 

 are able to live; their external and internal structure will be 

 described below (chap. 13). 



Fanerophytes occur in comparatively few of the natural 

 orders represented in Transcaspia (Table 5). For instance 

 in Borraginaceae, Caryophyllaceae, Cruciferae, Labiatae, Ranun- 

 cnlaceae and Umbelliferae they are totally absent. On the 

 other hand, the numerous species of Tamarix and Calligonum 

 have this effect that the Tamaricaceae and Polygonaceae 

 consist mainly of trees and bushes. The species of Calli- 

 gonum are more especially true desert-plants. Many of the 

 fanerophytic Papilionaceae (Astragalus, Ammodendron , Ere- 

 mosparton) and Chenopodiaceae (Salsola, Haloxylon), are like- 

 wise true desert plants, xerophytic in structure. On the 

 contrary the only two fanerophytic Compositae (Artemisia 

 procera and Zollikoferia acanthodes) are unimportant species, 

 rarely recorded. 



The 10 per ct. of Geophytes in the Transcaspian desert 

 is a rather high figure compared with the "Normal - Spec- 

 trum", but it is in agreement with Samos and Cyrenaica 

 (Table 3). Of the 72 geophytes, 33 (46 per ct.) are rhizome- 

 plants, 24 (33 per ct.) are bulbous plants, 9 tuberous plants 

 (13 per ct.), and 6 parasites (8 per ct., Orobancheaceae). 



As far as known only 5 geophytes may be found flowering 

 after July 1. Only one of these Eremurus Olgae is a bulb- 

 ous plant. The others (Tournefortia sibirica, Pluchea caspica, 

 Cressa cretica, Saccharum spontaneum) have rhizomes. The 

 term early flowering when applied to the rhizome-geophytes 

 does not indicate that the epigeal shoots die after that time, 

 for they continue to vegetate e. g. in Heliotropium Radula 

 and chorassanicum, Acroptilon, Dodartia, Aristida and Elymus. 

 Bulbous and tuberous plants, on the contrary, almost all 



