334 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



for air or some other gas? If the gas were in part steam, as seems 

 plausible and likely, condensation began when the lava cooled suffi- 

 ciently, and the cavities became moist but may not have filled up im- 

 mediately with watery solutions. Granted such conditions, it is easy 

 to visualize filaments growing as helictites from the moist walls of 

 the unfilled cavities. Perhaps some did so; but, compared with the 

 rather simple natural helictites, the thunder-egg filaments, in their 

 great variety and delicacy, their intricate interconnecting branching 

 networks (pi. 5, figs. 3, 4), and in other features to be discussed, give 

 the definite impression that they did not originate as helictites but 

 grew from any part of the surrounding wall into solutions that, early 

 or late, filled the original cavities. 



This probability leads to a consideration of the properties and be- 

 havior of artificial chemical gardens, special kinds of which are called 

 silicate gardens. Anyone with a few chemicals and the application 

 of care and patience can produce these interesting, beautiful, and 

 instructive cultures. For example, pour some waterglass or sodium 

 silicate (many other media are now known to be usable) into a beaker. 

 Then drop into the solution small grains of metallic salts, such as those 

 of calcium, cobalt, copper, iron, manganese, nickel, uranium, and 

 others. The more soluble the salt the quicker the result. Shortly, the 

 garden will start to grow, the "seeds" sprouting tubular branched or 

 unbranched filaments remarkably similar to the growths in thunder- 

 eggs. These and other chemical gardens have been known for a long 

 time and have been quite ardently investigated, fairly well illustrated, 

 and satisfactorily explained (Gradenowitz, 1907; Leduc, 1911; Lillie, 

 1917, 1922 ; Lillie and Johnston, 1919 ; Hazelhurst, 1941) . In his book 

 The Breath of Life, John Burroughs (1924, p. 167) refers to these 

 experiments: "The chemists have played upon this tendency in the 

 inorganic to parody or simulate some of the forms of living matter. A 

 noted European chemist, Dr. [Stephane] Leduc, has produced what he 

 calls 'osmotic growths' from purely unorganized mineral matter — 

 growths in form like seaweed, polyps, corals, and trees." Aside from 

 the light these experiments shed on the plantlike structures in thunder- 

 eggs, they provide stimulating comparisons with some of the growth 

 forms and processes in plants and animals and possibly contain clues to 

 the origin of life itself (Leduc, 1911; Lillie, 1922; Thompson, 1948). 

 Through all the recent investigations of these chemical precipitates has 

 run a persistent attention to the electrical factors and effects. 



SEQUENCE OF EVENTS IN THUNDER-EGGS 



That the genesis of the pseudoalgae in thunder-eggs is comparable 

 to that of silicate gardens rather than to helictites seems believable, 

 for it is in accord with all the known facts. In defense of this conclu- 



