On Dendritic Figures. 345 



frame work of the wings of insects consists of a solid horny 

 substance. 



For the advancement of natural knowledge, and for the im- 

 provement of organic physiology, it may be useful to collect 

 and to collate various evidences, in order to establish the laws 

 which direct the formation of similar figures in different bodies. 



In many cases the progressive steps of physical causation are 

 more apparent in mineral bodies than in the complicated and 

 living structures of animals and vegetables ; and these examples 

 of resembling figures will, therefore, commence with minerals 

 which present dendritic figures, uninfluenced by the disturbing 

 actions of vitality. 



The most simple, and one of the most common examples of 

 dendritic figures, occurs in the manufacture of the cheapest 

 sort of ornamented pottery ware termed the '* Mocha pattern.' » 

 These picturesque figures are made by children who are entirely 

 ignorant of the art of design. While the vessel is in the unglazed 

 state termed Biscuit, it is dabbed in given places with a liquid 

 pigment which runs by descent, as the surface of the vessel is 

 inclined, and thus it instantly spreads from trunks into regular 

 subdividing branches ; the rough surface of the biscuit, and the 

 gradual thickening of the liquid pigment, producing these ap- 

 pearances. 



Streamlets similarly divaricating appear on the sea- shore 

 where little pools of wat: v remain embanked by sand. The 

 water oozing through the sand issues in streams, and these sub- 

 divide, according to the declivity, into arborescing streamlets, 

 which sometimes again reunite into larger branches, as in the 

 anastomoses, between arteries and veins of animal structures. 

 The same appearances often occur upon clayey or muddy de- 

 clivities over which streamlets of water flow. 



Dendritic figures are also common in many stones which were 

 formerly regarded as petrifactions of previously organized 

 structures. In the compact marly limestone, called Lithogra- 

 phic stone, these figures often occur, and generally on the sur- 

 faces of laminae, by which it would seem that the ochry pig- 

 ment had percolated and spread in the same manner as that 

 described respecting pottery. The moss-agate, certain marbles, 

 and mocha-stone, exhibit similar dendritic figures. The entire 



VOL. XXVI. NO. LII. APRIL 1839- Z 



