BOG XEROPHYTES AND ACID SOILS. 



115 



vegetation of the Paramos in contrast with that of the Punas. This 

 is all the more striking, since the vegetation of the first has in the 

 main an evident xerophilous character. This is due not only to the 

 amount of soil-water, but also to other conditions. Sachs has shown 

 long ago that the absorption of water from the soil was related to the 

 presence of a proper temperature. Plants can wilt in a soil rich in 

 water if the absorption of the roots on account of the low temper- 

 ature is less than the water-loss. In the Paramos the cooling-off 

 of the soil is significant and the change in temperature rapid, while 

 the warming-up through the sun lasts only a short time and is of little 

 effect in the wet spots. About 11 o'clock the Paramos are usually 

 shrouded in cloud and fog, and the sun indeed is often hidden before 

 this time. The roots, as a consequence, grow in a soil almost always 

 cold, and the absorption of water is relatively small. On the other 

 hand, transpiration is increased by the strong winds and the rarefied 

 air. These factors work together to explain the peculiar fact that 

 xerophilous vegetation occurs in habitats that are rather to be called 

 wet than dry. Thus, the thick woolly Espeletia and Culcitium were 

 not rarely found in the middle of swamps. Meigen (1894) sup- 

 ported the views of Kihlmann and Goebel as to the causes of the 

 xerophytic characters of swamp plants. 



Warming (1895, 1896, 1909 : 193) enumerated the following swamp 

 species which exhibit xeromorphy to the extent that they are pro- 

 tected by certain devices from desiccation : 



Hairy coating: 



Ledum grcenlandicum. 

 palustre. 



Salix glauca. 

 lanata. 



Cassandra calyculata. 



Nyssa uniflora. 



Persea pubescena. 



Magnolia viiginiana. 

 Stomatal papilla: 



Carex limosa. 

 panicea. 

 rariflora. 



Lysimachia thyrsiflora. 



Polygonum amphibium. 

 Waxy coating: 



Vaccinium uliginosum. 



Andromeda polifolia. 



Vaccinium oxycoccus. 



Salix grcenlandica. 



Acer rubrum. 



Persea pubescens. 



Waxy coating — con.: 



Carex panicea. 



Primula farinosa. 

 Thick cuticle: 



Scirpus. 

 Leathery leaves: 



Andromeda polifolia. 



Vaccinium oxycoccus. 

 vitis-idsea. 



Ledum palustre. 

 Mucilage: 



Berchemia scandena. 



Pieris nitida. 

 Ericoid leaves: 



Erica tetralix. 



Calluna vulgaris. 



Empetrum nigrum. 

 Juncoid leaves and stems: 



Equisetum limosum. 



Junci genuini. 



Scirpus coespitosus. 

 lacustris. 

 palustria. 



Juncoid leaves and stems — con. 



Eriophorum vaginatum. 



Carex microglochin. 

 diceca. 



chordorrhiza. 

 pauciflora. 

 Erect or equitant leaves: 



Iris. 



Narthecium. 



Acorus. 



Xyris. 



Alisma plantago. 



Sagittaria latifolia. 



Butomus. 



Typha. 



Sparganium. 



Ranunculus lingua. 



Lathyrus nissolia. 

 Closure of leaves: 



Carex goodenowii. 



Warming regards it as evident that there must be a causal connec- 

 tion between the soil and the xeromorphic structures, i. e., the soil 

 must be physiologically dry, and hence some of the conditions under 

 which marsh-plants live compel them to conserve water. The va- 

 rious factors thought to be concerned and often to cooperate are: 



