THE FLORAL ENVIRONMENT 59 



of this group are particularly common in the semi- 

 deserts and deserts of Palestine, Sinai, Persia, and 

 indeed in most parts of the Great Palsearctic Desert. 

 Many of them belong to the Lily, Amaryllis, and 

 Iris famiUes, and famihar examples are colchicum, 

 squills (the broad leaves of which are shown on the 

 right in Fig. 26), tuHps, asphodels, onions, and stars 

 of Bethlehem. Their reserves of food are stored in 

 different parts of the plant : in Stars of Bethlehem 

 (Ornithogallum), onion (Alhum), and others, in 

 closely packed leaf -bases constituting a bulb ; in 

 iris, crocus, etc., in swollen subterranean stems 

 (corms) ; and in the roots in asphodels and others. 



The third important group in the flora contains 

 those perennial forms which are so specialized that 

 they can exist above ground and perform their vital 

 functions at all seasons. To this end they are 

 modified in many remarkable ways ; roughly speak- 

 ing, the modifications fall within two groups, those 

 which tend to reduce the loss of water from the 

 surface of the plant, and those which tend to preserve 

 a store of water in the body of the plant. Many 

 forms exhibit both types of modification. In the 

 first group of adjustments to environment we find 

 that the leaves are small or absent, or only produced 

 after rain when the soil and the air are relatively 

 damp ; at such times loss of water from the surface 

 of the leaf is of less importance than during the dry 

 season. In those plants in which the leaves are 

 greatly reduced or absent the twigs and stems are 

 green ; it is the chlorophyl in these organs which 

 carries on the function of starch manufacture, a 



