170 FOOTNOTES FROM 



that they completely cover the original plants, and hide 

 their forms from view ; while at other times they are 

 confined to the extremity of the branches, or form con- 

 centric circles around their base and middle. They con- 

 sist of simple or branched filaments, sometimes aggregated 

 into thick radiating tufts, like a thick tassel held up- 

 wards, each thread or filament measuring from the 

 swu^h ^ ^ ne iV'k f an i ncn * a l en gth, and from 

 the soooo^h to the 2 5 o o o^h f an ^ nc ^ ^ n diameter. 

 Some of these seem to be articulated, and to contain 

 spores or germs between the joints ; but owing to their 

 exceedingly minute size, the power of the microscope in 

 its present condition is not sufficient to resolve them into 

 their component parts, and of their processes of growth 

 and propagation we know absolutely nothing. They 

 tremble on the extremest verge of the horizon of human 

 knowledge, like the remotest fixed stars in heaven ; and 

 whatever proof of design they may present in their struc- 

 ture and functions, it is not intended for our ken ; for 

 Nature jealously guards the secrets of her inmost shrine, 

 and forbids her most ardent votary to approach beyond 

 the threshold. 



But the most extraordinary of all the members of 

 this numerous and highly varied family of plants are 

 the diatoms or brittle- worts, which form a wonderful 

 microcosm of their own ; an impenum in imperio. 

 It is but a few years since the miscroscope has drawn 

 aside the veil which hid them from our view, but our 

 knowledge of them, thanks to the all-absorbing at- 

 tention with which scientific men have regarded them, 

 is already remarkably extensive and accurate. Though 



