280 



»corlical» and »epidermaU layers. The culting olT of Ihe super- 

 licial cells is seen in lig. 1 b. They form Ihe assimilalory layer 

 and have numerous disc-shaped chloroplasls, dilficult lo see in 

 preserved material, \vhere all Ihese cells are filled \vilh a dark 

 broNvn substance. The slage seen in lig. 1 c seems lo be Ihe final 

 one as I do nol believe that Ihe wall surrounding Ihe thallus cavily 

 increases much more in thickness. Mitchell and Whittixg speak 

 of two epidermal layers, bul I fmd only one. 



Below the subepidermal layers the cells become larger and less 

 regular, forming a Iransilion to the filamentous network of the 

 thallus; these cells stretch themselves, become separated and add 

 new elements to the large branched central filaments. Intercalary 

 divisions occur in this region (lig. 1 a). The last stage is reached 

 by the formation of innumerable hyphae. The interspace is filled 

 with mucilage. 



According to Mitchell and Whitting the outer layers keep pace 

 with the inner ones through radial divisions. I do not believe that 

 radial divisions take place. If we study fig. 1 o and the figures of 

 RoE it will appear that in the young apex the filamentous structure 

 can be followed right through; the end cells have not originated by 

 radial divisions, but are branches from the supporting cell, and the 

 end cell often grows out to form a hair. The large central filaments 

 can be followed through the whole length of the thallus (fig. 2). 

 There seem to be several primary filaments, branching di- or 

 trichotomously. The same structure is repeated in the branches. 



So far as 1 can see, the thallus has attained its definite thick- 

 ness a little below the apex, where the colour suddenly gets darker; 

 accordingly the apex is very broadly vaulted. 



Thus, I conclude that Splachnidiiim is filamentous and the cortex 

 pseudoparenchj^matous; the filaments are repeatedly branched and 

 may end in a hair of the Phaeosporean type, which is of short 

 duration. The end cells together form the meristematic zone and 

 build up the cortex by branching and dividing by cross w^alls; the 

 lower cells become elongated and give rise to medullary tissue. 

 This is an ectocarpoid structure, very different from the laminaroid 

 or fucaceous one, attributed to this plant by previous authors. We 

 find essentially the same structure in the Chordariaceae. It is to 

 be regretted that the earliest stages of the main shoots have not 

 been found, but with the facts at hand I feel justified in regarding 

 Splachnidiam as a Chordariaceous type. The lower part of the hairs 



