56 FOOTNOTES FROM 



deserts of central South America, among aloes and cac- 

 tuses, is possessed of remarkable hygrometric properties. 

 In the dry season, when every particle of moisture is ex- 

 tracted from the soil, it detaches itself from its growing 

 place, rolls itself up into a ball, like the young frond of 

 a fern before it is unfolded, and is carried away by the 

 violent equinoctial winds which prevail at the time in 

 these regions, often to very great distances. It remains 

 coiled up in this form for a considerable time ; but if 

 carried to a marsh or the margin of a stream, or any 

 other moist place, it begins slowly to unfold, and spreads 

 itself out flatly on the soil like a branch of arbor-vitse, 

 assumes its former vigour and freshness, takes root, de- 

 velops its fructification, and casts abroad its seed upon 

 the air. When this new situation is dried up, it resumes 

 its old nomadic habits, and like an adventurous pilgrim 

 takes advantage of the wind to emigrate to a more favour- 

 able locality. A singular phenomenon has been observed 

 in a species of selaginella cultivated in Kew gardens, 

 called specifically from this circumstance mirabilis. " In 

 the morning the fronds are green, but as the day ad- 

 vances they become pale, recovering gradually their colour 

 by the following day. Dr. Hooker has observed that in 

 their pale condition the endochrome of the cells of the 

 leaves is contracted into a little pellet." 



The club-mosses bear in the axils of their leaves 

 minute round or kidney-shaped cases of a bright yellow 

 colour, which form the receptacles of their dust-like seed. 

 Some species have little cone-like spikes at the tips of 

 their branches, under the scales of which, as in the pine 

 tribe, lurk the reproductive embryos. In the common 



