Schrader : observations on alaria nana. 161 



of certain rows of cambial cells, situated between the inner and 

 outer cortex. This difference in outer and inner cortex, caused 

 by this radial growth of the outer cortex, seems to the writer, to 

 account for the growth rings figured by Postels and Ruprecht. 

 Growth in thickness is also due to the activity of these cambial 

 cells. 



Young stipes are rather soft, but older ones are quite tough 

 and hard, although in this respect they are comparable to stipes of 

 Laminaria rather than to those of Lessonia or Pterygophora. 



The Lamina. — In Alaria the lamina is provided with a very 

 distinct midrib, which is practically a flattened extension of the 

 stipe. The lamina proper, may be compared to a flattened ex- 

 pansion of the midrib {Jig. 22). 



As in the stipe, a medullary or pith area is found in the mid- 

 rib, but no distinction into outer and inner cortex can be made 

 out. In a cross-section the pith area will appear very similar 

 to that of the stipe, except that it is much looser {Jig. 25) but 

 the cortex will be seen to consist of fairly regular, polyhedral 

 cells of medium size, and tightly packed {Jig. 23). Chloro- 

 plasts seem to be present only in the outermost layers, as in the 

 case of the stipe {Jig. 24). When a section of the lamina {Jig. 

 26) perpendicular to the midrib, and close to it, is examined, it 

 is readily seen that the lamina is morphologically but an expan- 

 sion of the midrib, for the epidermis and cortex differ from the 

 same areas in the midrib in no respect whatever, but the inner 

 layers of cells gradually become very much elongated and tend 

 to anastomose at their ends. In sections taken parallel to the 

 midrib, and at some distance from it {Jig. 2j) it is seen that 

 practically all the tissue except the epidermis consists of long 

 anastomosing cells which are cut at various angles owing to 

 their position. This portion of the plant is very gelatinous, and 

 as soon as decay sets in bladders of mucilage are formed all 

 over its surface by the decay of the tissue. 



The meristem or growing area in Alaria is at the junction of 

 the stipe and the lamina. The lamina, therefore, grows at its 

 lower end, and the stipe at its upper end. This is also shown 

 by the fact that the base of the lamina is usually elastic, while 

 the tip, which is older, is more flabby and gelatinous. 



The gonidiophylls arise at the upper end of the stipe, just 

 below the meristematic area. They first appear as little conical 

 outgrowths of the stipe, but flatten out very soon {Jigs. 4, 5, 



