LICHENS 521 



and subalpine districts. Many bright vermilion-red tubercles grow 

 from the edge of the funnel-shaped upper portion of the stem. 

 These tubercles closely resemble the perithecia of certain fungi, 

 and if a thin section through one is examined under the microscope 

 the asci containing spores can be seen. 



Cladonia rangiferina (reindeer moss). — This is a very common 

 lichen on heaths in lowland, subalpine and Alpine districts, grow- 

 ing on the gi-ound. In this country it varies from 3-6 in. in height, 



Cladonia pyx id at a 



pale greenish grey or sometimes almost straw-colour. Like the 

 grasses, it is a social plant, and in Lapland covers vast tracts of 

 country, and growing to a height of 6-12 in. In winter it practi- 

 cally forms the only food of the reindeer, who clear away the snow 

 by means of their horns to browse on the lichen. It is also collected 

 as fodder for cattle. 



Other species closely resembling the present grow on the ground 

 on our heaths and 'moors. 



Cladonia pyxidata. — One of the commonest and at the same 

 time, within certain limits, one of the most variable of lichens. 



