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desert; as the distribution of the growth-forms of the species 
of larger families are here given as percentages. The orders 
which are especially represented by annual species are the 
Cruciferae and the Chenopodiaceae, the percentage of these 
being respectively 90 and 72. Of these the Cruciferae are 
all early flowering ephemerals, whereas about 82 per ct. of 
the annual Chenopodiaceae are summer-plants which flower 
after the beginning of July. A large proportion of the early 
flowering annual Chenopodiaceae also live far into the summer. 
These two families, the Cruciferae and the Chenopodiaceae 
are thus typical representatives of two widely different 
series of adaptations to desert-life: the one shows itself in 
the quick development of plants of mesophytic structure 
during the favourable season; the other is characterised by 
slow development combined with the power to withstand the 
unfavourable conditions of the dry season. The former series 
include all the other families in table 5 with a large number 
of annual plants, e. g. Borraginaceae, Gramineae and Ranuncul- 
aceae. Outside the Chenopodiaceae there are very few annual 
summer-plants. 
That the adaptation of the ephemeral planfs is advan- 
lageous is easily seen; the continuity of the race is ensured 
with a slight expenditure of material. Life with these plants 
seems a much simpler matter than in the case of the annual 
summer-plants which have to contend with a long hot 
summer before their seeds are ripened. The existence of the 
latter is far more expensive, because for one thing material 
must be produced for the development of mechanical, water- 
storing, and other specialised tissues which the ephemerals 
do not require; moreover many of the annual summer-plants 
do not complete their natural span of life because they are 
buried by the sand, or the soil blows away, or they die 
of thirst. 
In this connection attention is drawn to the outstanding 
difference between the mode of occurrence of the ephemerals 
and the annual summer-plants. As already described, the 
former often appear in masses during spring, while the latter 
almost always occur as single plants standing widely apart. 
This is of course largely due to the greater number of 
