1918 Frye; on Pterygophora 67 



shows the same thing, but the exact spot is even more difficult to fix 

 in such a section. This could only signify that the rings are formed 1 

 per year. 



A third evidence is the fact that in June and July the outer ring is 

 thin and evidently incomplete (Fig. 6), but not so in November. This 

 might be true of 1 kelp or of several but hardly of all, unless the ring is 

 conceived to be only partially completed. The ocean is much more uniform 

 in growing conditions than the land. There are no marine dry years to 

 affect kelp> as there are on land to affect trees. 



Thus it appears that 3 different lines of observation all point in the 

 same direction ; viz., to annual growth rings in Pterygophora californica. 



How old these kelps get is not yet certainly known. The writer has 

 found none over 5 cm. in diameter at 2.5 cm. from the base. The maxi- 

 mum number of rings counted was 21. MacMillan (1902) reports some 

 stalks 7.5 cm. in diameter, without stating the number of rings. The 

 maximum number of rings reported in Pterygophora by MacMillan (1902) 

 is 24, in a kelp stalk 5 cm. in diameter. We have thus fairly good evidence 

 that certain kelps live for nearly a quarter of a century. 



A peculiarity, tho unrelated to the facts above, should be noted. One 

 jilant was found which had its central blade split through the growing 

 region about 3 or 4 \'ears before examination and one of the parts again 

 1 year before examination (Fig. 9). Half the plant, from the original 

 split, formed blades on both sides after a time. The other half did not. 

 The region of blade formation is evidently not fixed at the original mar- 

 gins. The half which formed blades on 1 side only had its rib near one 

 side (Fig. 9, right side); the other half split again, but one of the parts 

 had a central rib. 



Also a plant was found growing upon another (Fig. 7). The holdfast 

 of the epiphyte (Fig. 7, c), evidently induced the formation of haptcres 

 in the other at this point about 6 cm. up the stalk (Fig. 8). Possibly 

 contact induces the formation of holdfasts in abnormal positions. The 

 writer observed a similar thing in Nereocystis luetkeana in 1913 (Frye, 

 1915). In that case, which was })hotographed but not explained, the hold- 

 fasts were believed to be due to a wra))ping of filamentous red algae. 



Certain other kel]:)S show growth rings. Alaria trriiiifolia grows 

 abundantly at l-riday Harbor, Washington. Old stalks show growth 

 rings. Some of these were cursorily examined in connection with this 

 work. A. tenui folia on the rocks near low tide showed in the oldest look- 

 ing specimens 1-4 rings near the base; but gradually fewer upward on 

 the stalk, until there was only 1 at the top. Near by, a floating dock 

 had fine large A. tenuifolia on it, but not one among a dozen tried con- 



