158 MINNESOTA BOTANICAL STUDIES. 



cal specimens were but thirty-two and forty-two centimeters 

 long, respectively, and the largest specimen seen was not more 

 than a third longer than this. 



In all these specimens, a root or holdfast area, and a shoot, 

 or stipe and lamina area, could be made out. The broad 

 characteristic midrib was present in all, and even in the smallest 

 specimens collected, it was just as wide and thick, comparatively 

 speaking, as in the largest plants. The presence of this mid- 

 rib makes it easy for a collector to determine whether he is 

 handling an Alaria or another kelp. 



The following figures give the measurements in centimeters 

 of four typical young plants, and of two of the largest speci- 

 mens collected. 



Plant number, i. 2. 3. 4. 5. 6. 



Total length, 3. 1.5 4. 5.5 42. 32. 



Length of stipe area including rachis, .75 .4 .75 1.5 10. 6. 



Width of lamina, i. .6 1.75 3.2 8. 6.5 



Width of midrib, .3 .1 .3 .5 .75 .6 



Length of gonidiophyll, * 10.2 8. 

 Width of gonidiophyll, 2.55 2.25 



Number of gonidiophylls, 44. 32. 



Alaria is unbranched and the chief difference between a 

 young and a mature plant is the absence of gonidiophylls in 

 the former. The largest specimen collected was but forty-two 

 centimeters long, rather small, when one considers that speci- 

 mens of other species, six feet or more in length, may be found 

 less than a hundred yards away. In healthy specimens the 

 tissue of the lamina is elastic and thin, but when the plant gets 

 older, portions of the lamina begin to decay, forming large 

 bladders of mucilage all over the surface. Perfect mature 

 specimens are seldom if ever found, owing to the violent beat- 

 ing of the surf on the rocks to which they are attached. 



The holdfast area is well developed in this Alaria. In the 

 youngest plants collected, it consists merely of a small disc- 

 shaped area, very little wider than the diameter of the stipe. 

 Above this disc-shaped portion a few hapteric branches grow 

 out from the base of the stipe. In larger specimens there are a 

 great number of these hapteres. They are brown in color, 

 branch dichotomously, and their tips are flattened somewhat 

 where they clasp the rocks. These hapteres form a dense and 

 solid network, between the meshes of which the young plants 

 find a secure foothold. 



* Two gonidiophylls appearing on upper portion of stipe. 



