0? ARTS AND SCIENCES. 



193 



saccharina.* Kiitzingf figures and describes young plants of Lami- 

 itaria saccharina consisting of a simple membrane. I have seen a 

 young plant, probably belonging to Laminaria PhylUlis, (Stackh.) 

 J. Ag., which consisted of a simple filament. 



It seems fairly certain, then, that the germinating zoospore of the 

 LaminariecB gives rise first to a simple filament, and later to a simple 

 membrane ; and it seems very probable also that the earliest stages 

 of Saccorlnza dermatodea will be found to correspond very closely 

 to those known for Saccorhiza bidbosa. 



Second Period. — The preceding period is doubtless very short, and 

 changes soon begin which convert the simple membrane into a mem- 

 branaceous frond of more complex structure. The changes take place 

 in the early portion of what has been marked off as the second period 

 of the development. The youngest specimens m my possession show 

 these changes already well advanced, and have been partially de- 

 scribed above in the account of the morphology. They are of very 

 delicate consistency, and are therefore difficult to manipulate. Fur- 

 thermore, there were only two or three of the very small ones, and 

 on these accounts many of the details of the histology here given had 

 to be derived from somewhat older plants, belonging however to the 

 same period. 



When one of the youngest plants is examined under a low power 

 (150 diameters), it is seen that the stipe and the midrib-like portion 

 of the blade have already arrived at some degree of complexity of 

 structure. The outline of this midrib portion, as mentioned above, is 

 irregular (cf. Figs. 1 and 2). In Figure 1 it is seen to have several 

 tooth-like projections from the main portion. One of these (labelled A) 

 is situated at the tip. Somewhat below, at A', there is another one, 

 and at A" still another. These are only more prominent than the 

 others at A'", and so on, but do not differ in kind. At the very 

 tip the blade is eroded, and consequently we find here, as has been 

 described for other LaminariecB, that the growth is not apical, but 

 from below, and that the apex of the blade is the oldest portion. As 

 a still further evidence of this, it can be seen that the apical portion of 

 the blade is of simpler structure, and becomes more complex down- 

 ward. This is exactly what we should expect from what we know 

 from other members of the group. Consequently, a set of transverse 

 sections of one of the plants, arranged in a series from above down- 



* Ann. Sci. Nat, Ser. 3, Tom. XIV. PI. 30, Figs. 1-4. 

 t Phyc. Gen., p. 345, Taf. 24, I, Fig. 5, 1843. 

 VOL. XXVI. (n. s. xviii.) 13 



