— 258 — 
the large number of spring-plants with light-shoots which 
only live a short time, and also the chamaephytes and 
fanerophytes on which annual shoots are common, but 
where the persistent shoots of most species lose their distal 
parts. 
2. Reduction of the leaves. It is a well-known feature 
of deserts that the leaves become small or disappear entirely. 
As a rule the stem assumes the part of vicar, it may be in 
some cases where leaves are still present, as assistant vicar, 
or in other cases, where leaves are entirely wanting, as 
deputy-vicar (B. Jonsson 1910). Borrtvanr has proved by 
experiments a correlation between absence of leaves and 
formation of assimilating tissue in the stem. 
3. The frequency of the centric type of assimilating 
organs (in and outwith the Chenopodiaceae) and of isolateral 
leaves. Isolateral structure seems to be specially dependent 
on strong light (HEINRICHER), and it must promote the process 
of assimilation. The xerophytic structure of the assimilating 
organs is likewise a well-known feature in desert plants as 
recorded in the various text-books on plant-geography; see 
also HENSLOW 1893, with whose interpretation, however, I 
do not agree. 
SECTION" IV. THE: FLORA“ OF THE 
TRANSCASPIAN LOWLANDS. 
CHAPTER 14 
The Elements of the Flora. 
When at the beginning of the Quaternary period Trans- 
caspia emerged from the sea which retreated towards the 
West and North, a change in climatic conditions took place 
simultaneously in the various parts of Western Asia previously 
