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Puget Sound Marine Sta. Pub. 



Vol. 1, No. 13 



siderable size, the more nearly the sporophylls reached the stage of mature 

 zoospores, the slower the rate of growth, until when that stage was reached 

 the growth ceased. When the tip of such a sporophyll contained no zoo- 

 spores it became ragged and worn off. In connection with periodic regen- 

 eration in Laminaria Setchell (2) emphasized the passing of the whole 

 plant into a state of rest at the time of fruiting. In the same paper he 

 adds: "Other species of this group, particularly of Laminaria, show sim- 

 ilar contrasts between the earlier vegetative stages and the fruiting ones. 

 The latter show thicker, darker-colored fronds, and the fact that active 

 growth has stopped, is shown by the ceasing of increase in length for the 

 stipe and the actual shortening of the blade, since the erosion at the sum- 

 mit is no longer made good by an increase from below." The slow rate 

 of growth in the spore-forming blades of all of the kelps was observed. 

 For example, one plant of Cymathere in which mature gametes or zoo- 

 spores were found, increased from 30 cm. to only 30.7 cm. from July 17 

 to Aug. 6. A maturing blade of Laminaria increased from 40 cm. to only 

 40.7 cm. from July 25 to Aug. 5. Again, a blade of Agarum with repro- 

 ducing patches increased from 30 cm. to only 30.9 cm. between July 25th 

 and August 6. 



The daily study of the kelps during the eight weeks of observations, 

 made it possible for the writer to pick out the healthy growing plants by 

 their color and texture. It is with them just as it is with the leaves of a 

 tree, the more recent growth being lighter in color, and softer and more 

 delicate in texture. The tips of the blades, where there is very little or 

 no grow^th, are darker and duller ; that is, they lack that soft, almost trans- 

 parent new look that the growing portions have. The blades with fruiting 

 patches can also be easily distinguished by their slight difference in color. 

 MacMillan (7) refers to the fruiting patches of Nereocystis as being 

 very conspicuous on account of their slightly lighter color than the sterile 

 tissue. 



Table 4. Shoxcing ihe gain in cm. of length during 8 consecutive days and 

 nights for 5 species of kelp. 



Nereocystis 



Laminaria 



A a II rum 



Observations showed that the growth during the day was almost 

 double that at night. On eight consecutive days measurements were made 



