THE SMITHSONIAN INSTITUTION. 93 



causing a weaker acid to unite witli the base. Thus they decompose 

 the muriate of soda which they absorb from sea-water, })artly freeing 

 and partly apiiropriating the chlorine and hydrogen ; and the soda 

 is found combined in their tissues with carbonic acid. 



A remarkable instance of the action of a minute Alga on a chemi- 

 cal solution was pointed out to me by Prof. Bache, as occurring in 

 the vessels of sulphate of co})per kept in the electrotyping department 

 of the Coast Survey office at Washington. A slender confervoid Alga 

 infests the vats containing sulphate of copper, and proves very 

 destructive. It decomposes the salt, and assimilates the sulphuric 

 acid^ rejecting (as indigestible !) the copper, which is deposited round 

 its threads in a metallic form. It sometimes appears in great quan- 

 tities, and is very troublesome ; but the vats had been cleaned a few 

 days before I visited them, so that I lost the opportunity of examining 

 more minutely this curious little plant. Most probably it is a spe- 

 cies of Hi/grocrocis,* a group of Alga3 of low organization but strong 

 digestive powers, developed in various chemical solutions or in the 

 waters of mineral springs. All the Alga?, however, which are found 

 in such localities are not species of Hygrocrocis, for several Oscillatorice 

 and Calothrices occur in thermal waters. Species of the former genus 

 are found even in the boiling waters of the Icelandic Geysers. Of 

 the latter, one species at least, Calofhrix nivea, is very common in 

 hot sulphur springs, and I observed it in great plenty in the streams 

 running from the inflammable springs at Niagara. 



But on whatever substance the Alga may feed, it is rarely obtained 

 through the intervention of a root. Dissolved in the water that 

 bathes the whole frond, the food is imbibed equally through all the 

 cells of the surface^ and passes from cell to cell towards tliose parts 

 that are more actively assimilating, or growing more rapidly. The 

 root, where such an organ exists, is a mere holdl'ast, intended to keep 

 the plant fixed to a base, and prevent its being driven about by the 

 action of the v/aves. It is ordinarily a simple disc, or conical expan- 

 sion of the base of the stem, strongly applied and firmly adhering to 

 the substance on which the Alga grows. This is the usual form 

 an^ong all the smaller growing kinds. Where, however, as in the 

 gigantic Oar-weeds or Laminar ice, the frond attains a large size, 

 offering a proportionate resistance to the waves, the central disc is 

 strengthened by lateral holdfasts or discs formed at the bases of side 

 roots emitted by the lower part of the stem ; just as the tropical 

 Screw-pine (Pandanus) puts out cables and shrouds to enable its 

 slender stem to support the weight of the growing head of branches. 

 The branching roots of the Laminaria, then, are merely F'ucus-d'isca 

 become compound : instead of the conical base of a Fucus, formed of 

 a single disc, there is a conical base formed of a number of such discs 

 disposed in a circle. In some few instances, as in Macrocystis, the 

 grasping fibres of the root develop more extensively, and form a 

 matted stratum of considerable extent, from which many stems spring 



* Perhaps the Ilygrocrods cuprita, Kiitz, or some allied species ; but I had no opportunity 

 of examining a recent specimen, and the characters cannot be made out from a dried one. 



