12 A Fossil Alga. 



If we take as trustworthy only such cases as exhibit microscopic 

 evidence of minute structure, we have before us a scanty record of forms. 

 The earliest of all is the Nematophycus of Carruthers* from the Devonian, 

 which exhibits its structure so plainly that there need be no hesitation in 

 accepting the position assigned it by its author in the Udote<z, a sub-order 

 of SipJionece. In the same beds there is found another organism, 

 PachytJieca, described by Sir Joseph Hooker, f and others; but its claims 

 to rank with the Algae need a more cautious examination. Mr. Barber + 

 has recently described it in two papers. In the former he obviously and 

 confessedly mistook the microscopic evidence, and in the second giving a 

 detailed and accurate description of its structure, while avoiding ' theoretical 

 considerations concerning the systematic relations of the plant,' he assigns 

 it a place near Cladophora, I have recently examined the beautiful slides 

 of Pachytheca prepared by Mr. John Storrie, who most kindly placed them 

 at my service, with some hope that it might prove to be an encrusting 

 algal growth surrounding some spherical Alga, such as a Valonia, and 

 pushing its rhizoids within the sphere; but this view, which at one time 

 appeared to me a highly probable explanation, was abandoned after 

 repeated examinations and comparisons with living forms. I confess to 

 feeling as little attached to this view as to Mr. Barber's determination of it 

 (near Cladophora), which it would be hard to get a phycologist to accept. 



Its claims even to be reckoned an Alga may be regarded as still 

 doubtful. There is then a long break until we come to the Tertiary rocks, 

 in which besides the fossil Diatomacecs we have a series of Algae belonging 

 to the Dasycladece and other Siphonea described by Munier Chalmas, and 

 forms of Lithothamnion (Floridete), and several Characecz. These are those 

 which rest on the solid ground of structure, and the record is bare enough. 



It would be going too far, however, to restrict our view absolutely to 

 fossil Algae exhibiting such structure, or even to those possessing a rind of 

 coal, which Nathorst considers indispensable evidence. With regard to the 

 latter view it has been pointed out that coal ' may entirely disappear in the 

 course of time from remains that are undoubtedly organic, if they are 

 deposited in a porous rock.' || There are many fossil plants the deter- 

 mination of which is unquestionably correct, affording no other characters 

 than those given by impressions of outward form, and I may cite as a 



* Monthly Micr. Journ., 1872, vol. viii., p. 160 ; and 1873, vol. x., p. 208. 

 t Jotirn. Geol. Soc., 1853, p. 12 ; and Annals of Botany, vol. iii., No. x., 1889. 

 \ Annals of Botany, vol. iii., No. x.; also ibid., vol. v., No. xviii. 



Comptes Rendus de FAcad. des Sc., vol. Ixxxv. (1877), pp. 814-817. See also Bull. 

 Soc. Geol. de France, 3 sdr., vol. vii., p. 66 1. 



(I Graf zu Solms-Laubach. Fossil Botany, p. 47. 



