— 172 — 



we lind in certain tropical or semi-tropical deserts a far 

 greater percentage, thus in the Libyan desert 21 and at 

 Aden 27 per ct. (Raunki^k). This would seem to suggest 

 that the cold winter of the Transcaspian desert is unfavour- 

 able to the chamaephytes. 



It is known that aridity and heat favour ligniflcation 

 (Warming 1909 p. 127), and this may sufficiently explain the 

 occurrence of the chamaephytes — at any rate the under- 

 shrubs — in dry desert areas. That the Chamaephyte form 

 is in itself a favourable adaptation for the plants is not 

 directly obvious. Lignification and mechanical strength 

 must be favourable (Warming 1. c), and perhaps it may have 

 this effect that the assimilating shoots are removed from the 

 surface of the soil. 



The Cargophyllaceae, Chenopodiaceae and Papilionaceae 

 include proportionately the greater number of chamaephytes, 

 while most of the other orders in Table 5 have few or none. 



As to the 39 species of Aquatics and Marsh-plants 

 I can add nothing of special interest for Transcaspia. Besides 

 a number of Cyperaceae and Potamogetonaceae, the list in- 

 cludes plants like Valisneria spiralis, Lycopus europaeus, 

 Lemna, Najas, Epilobium hirsutum, Polygonum amphibium, 

 Salvinia, Typha. So far as the biological type is con- 

 cerned, there is nothing about these plants to characterise 

 them as especially Transcaspian. Something might be found 

 by a closer study of their finer adaptations, such as anatom- 

 ical structure, flowering, etc., an investigation I have not 

 attempted. 



The Aquatics and Marsh-plants are so far as known 

 early flowering, only 5 species flowering entirely or partially 

 after July 1. 



Summarising what has been said about the growth- 

 forms and their vegetative season, we may divide the growth- 

 forms into those characteristic for the xerophytic aspect (the 

 summer aspect), allowing at the same time that they may 

 live and vegetate in spring; and those which vegetate only 

 in spring and belong to the mesophytic aspect. 



The Xerophytic Aspect includes: 



