46 PENH ALLOW AND DAWSON 



Numerous large cavities were, nevertlieless, to be observed, indicating tbat the tissue of 

 the plant was not continuous, bn.t traversed in all directions by numerous intercellular 

 spaces. 



The lamiuœ are 0.25 mm. iu thickness, and sometimes they show a tendency to split 

 into two layers, as may readily be determined by a pocket lens. This would appear to 

 indicate the presence, originally, of two outer and firmer membranes, enclosing a central 

 layer of a less compact and resisting nature. Careful dissection showed that each one of 

 the original laminae can be wholly separated into two layers, each of which is similar to 

 the other iu its corresponding parts. 



An examination of the internal structure proved it to have been badly preserved ; 

 nevertheless, areas were obtained where the tissue was sufficiently well preserved to en- 

 able us to reach fairly definite conclusions as to the nature of the remains. 



The outer portions of the laminae show a distinctly reticulated structure, approxim- 

 ating to an epidermal tissue, but no organs which could be referred to as stomata, were 

 to be observed. In two instances out of several laminae examined, a few openings in the 

 structure were noted. These were narrowly elliptical, usually grou]ped within a narrow 

 radius — in one case, five were found in two well-defined rows. Their average size, as 

 determined from a measurement of six, was found to be 29.48 // X 86.36 ja Later 

 measurements of other openings have given a greater size — 52.6 |< X 105.2 jx When the 

 laminae are complete, the openings are found to penetrate the structure for only a portion 

 of its thickness, but when the former are split, the openings are then found to pass 

 through, or nearly through, the separated parts. From this it would appear that they 

 belong to the surface or cortical tissues, chiefly or wholly. 



The interior structure of the laminae consists of a mass of somewhat fine and num- 

 erously branching myceloid filaments, having a diameter of 1.59 /< — 2.12 /< with occa- 

 sional filaments of a coarser nature, having a diameter of 4.*7 /' There are also certain 

 indications that much larger and rather thick-walled filaments may have been present, 

 bixt of this we cannot be certain, as the structure is not sufficiently well defined. This 

 entire system of filaments appears to find its outward termination in a reticulated struc- 

 ture, constituting the superficial tissue already described. Although this structure is, in 

 most cases, destroyed, and, where preserved, difficult of determination, a very large num- 

 ber of examinations, under difierent conditions of illïimination, amplification and treat- 

 ment of the specimen, lead us to consider this as the true nature of the interior structure. 

 Moreover, instead of forming a compact structure, the interlacing filaments enclose a 

 large number of spaces or cavities, which are well defined and not to be mistaken. This, 

 therefore, coincides with the appearance presented by the ash skeleton. 



Both internally and externally, there is no trace of any vascular structure, and we 

 are at least justified in the conclusion that the organism was purely cellular. 



The structure thus described seems to indicate very strongly that our fossil must 

 have been an Alga, and from a careful examination of the larger seaweeds found on the 

 New England coast, we are led to consider it as allied to the Laminariae, of which the 

 genus Saccorhisa presents a structure with which it is fairly comparable, both with refer- 

 ence to its tissues and the openings or cryptostomata, which penetrate both surfaces 

 of the frond. With reference to these latter structures, the only essential difference is 

 one of size, the cryptostomata of Saccorhisa measuring 252.4 X 273.5 // 



