356 PROTOPLASMIC CONTINUITY IN THE FUCACE;E. 



In examiiiiug these tissues for evidences of the continuity of 

 the protoplasm, great difficulties have been met with, greater even 

 than those encountered in the Fiici. Hence the results, though 

 conclusive as to the existence of continuity in the central and 

 cortical tissues, are not quite demonstrative as to its permanence, 

 nor as to its extension over the whole thallus. The methods 

 employed for preparing sections for examination were those already 

 described in detail, swelling and clarifying reagents being absolutely 

 indispensable. 



In good sections prepared by these methods, stained, &c., the 

 following details may be made out with tolerable ease : — 



1. The protoplasm of the filaments, fibres, and cortical cells is 

 certainly interrupted, in many cases, at the transverse partitions, 

 longitudinal contraction of the proloplasts having at least equalled 

 that in other directions. 



2. In other cases, however, there are indisputable phenomena 

 of continuity conforming to at least two of the types met with in 

 AscvpJiylhivi nodosum. Thus in the filaments and fibres of the 

 central tissue, as well as in the cortical cells, many instances are 

 met with in which the continuity is brought about directly by a 

 comparatively stout undivided cord of protoplasm. Others are to 

 be found, though scarcely more frequently, in which continuity is 

 effected by means of a sieve plate, in which case the pores are 

 either scattered over the whole plate or restricted to its margin. 

 There are also cases which give rise to the suspicion that continuity 

 is sometimes maintained by a single, central, attenuated, thread of 

 protoplasm, but a perfect demonstration of this can hardly be said 

 to have been obtained. 



With regard to the epidermal tissue, it must be admitted that 

 decisive preparations either for or against continuity are still a 

 desideratum. The best sections hitherto obtained seem to point to 

 previously existing connecting threads running from protoplast to 

 protoplast, but in none of them have such threads been found intact. 

 It may be that the modes of treatment are too rough for such 

 delicate structures as these, but in any case this point will require 

 further investigation. 



From what has been stated it will be obvious that in Hiiuanthalia 

 lorea the arrangements for continuity are either not so universal or 

 not so permanent as in the Fuci, or else they are more easily 

 destroyed. Taking all the circumstances of the case into careful 

 consideration, and giving due weight to the appearances presented 

 by the sections, even where the continuity is interrupted, the 

 writer regards the last of these possibilities as by far the most 

 probable one. 



Laminaria digitata Lamx. 



Though not usually classed with the Fucaced, Laminaria diijitata 

 may be dealt with here, seeing that in histological structure and 

 the phenomena of continuity it exhibits, it bears some resemblance 

 to the forms already considered. 



Sections through the thallus show that, both in the rounded 

 stipes and the flattened lamina, the tissues may be described as 



