THE SMITHSONIAN INSTITUTION. 105 



on the surface of the polar ice an unfrozen vegetation of minute Alga^ 

 finds an appropriate soil. There are species thus fitted to endure 

 all observed varieties of temperature. Moisture and air are tlie only- 

 essentials to the development of Algio. It has even been supposed that 

 the minute Diatomacecu whose bodies float through the higher regions 

 of the atmosphere, and fall as an impalpable dust on the rigging of 

 ships far out at sea, have been actually developed in the air ; fed on 

 the moisture semicondensed in clouds ; and carried about with these 

 ''lonely" wanderers. 



Wben this atmospheric dust was first noticed, naturalists conjectured 

 that the fragments of minute Alga? of which the microscope showed 

 it to be composed, had been carried up by ascending currents of air 

 either from the surface of pools, or from the dried bottoms of what had 

 been shallow lakes. But a different origin has recently been attribu- 

 ted to this precipitate of the atmosphere by Dr. F. Cohn, Professor 

 Ehrenberg, and others, who now regard it as evidence of the exist- 

 ence of organic life in the air itself! This opinion is founded on the 

 alleged fact, that atmospheric dust, collected in all latitudes, from the 

 equator to the circumpolar regions, consists of remains of the sarne 

 species, and that certain characteristic forms are always found in it, 

 and are rarely seen in any other place. Hence it is inferred that the 

 dust has a common origin, and its universal diffusion round the earth 

 points to the air itself as the proper abode of this singular fauna and 

 flora — for minute animals would seem to accompany and doubtless to 

 feed upon the vegetable atoms. If this be correct, and not an errone- 

 ous inference from a misunderstood phenomenon, it is one of the most 

 extraordinary facts connected with the distribution and maintenance 

 of organic life. 



If Alg;\i thus people the finely divided vapor that floats above our 

 heads, we shall be prepared to find them in all water condensed on 

 the earth. The species found on damp ground are numerous. These 

 are usually of the families Palmellacece and Nostocliacece. To the 

 latter belong the masses of semi-transparent green jelly so often seen 

 among fallen leaves on damp garden walks, after continued rains in 

 autumn and early winter. These jellies are popularly believed to fall 

 from the atmosphere, and by our forefathers were called /a/?cri stars* 

 If such be their origin, we are tempted to address them, with Corn- 

 w^all in King Lear : 



" Out, vile jelly ! where is thy lustre now ? " 



for certainly nothing can well be less star-like than a Nostoc, as it 

 lies on the ground. 



An appeal to the microscope reveals beauty indeed in this humble 

 plant, but gives no countenance to the popular belief of its meteoric 

 descent. It is closely related in structure to other species found under 

 dripping rocks and' in lakes, and ponds, and the only reason for re- 

 garding it as an aerial visitant is the suddenness of its appearance 

 after rain. * 



«■ Other suhstances besides Nostocs occasionally get this name. Masses of undeveloped 

 frog-spawn, for instance, dropped by buzzards and herons, pass for meteoric deposits. 



