146 



Puh. Puget Sound Biol. Sta. 



Vol. 2, No. 43 



all the light, was larger than the part of the sporeling that develops into 

 the plant body of those receiving only % of the light and of those receiv- 

 ing no light at all. At the end of the fourth week the order of size was 

 reversed. The sporelings receiving all the light were a third larger than 

 those receiving l/o light and twice as large as those receiving no light. 

 There appeared to be no difference in size between the sporlings receiv- 

 ing Yg light and those in total darkness. Those in total darkness had a 

 much lighter color than those receiving y^ light. Evidently the growth 

 of constantly submerged sporelings varies with the light. 



The sporelings receiving most light had a dark brown color. As the 

 light intensity was reduced, the color in the sporelings became lighter. 

 All conditions were as nearly as possible the same except light. The 

 larger size and better color of the sporeling in the light was previously 

 explained in the case of sporelings receiving insufficient light. In series 

 number 2 of the above, in which sporelings were exposed to the air one 

 hour each day as the water was changed, the following conditions were 

 tried : 



a. A bowl uncovered. 



b. A bowl permitting ^ light. 



c. A bowl permitting % light. 



d. A bowl permitting no light to enter. 



Table 4. Sporelings exposed to the air for one hour each day, 

 and having different light intensities 



Am'nt of light 

 received 



Total light 



% light 



% light 



No light 



Short hold-fast ; 

 50% of spore- 

 lings came loose 

 from substrata 



Some growth ; few 

 sporelings came 

 loose from slide 



Long hold-fast ; 



p r a c tically no 

 sporelings came 



loose from slide 



Long hold-fast ; no 



sporelings came 



loose from slide 



Growtli of plant 

 body 



Little growth of 

 plant body ; col- 

 or much lighter 



Little growth of 

 plant body ; col- 

 or pale 



Hold-fast branch- 

 ing ; some growtli 

 of plant body ; 

 color dark broTNTi 



Some branching of 

 hold-fast ; some 

 growth of plant 

 body 



No growth ; 

 very pale 



color 



Continued growth ; 

 color dark brown 



Slow growth con- 

 tinued and color 

 good 



No growth ; color 

 pale; cells 

 breaking down 



In this series (table 4) none of the sporelings were as large as were 

 the sporelings of the same age when submerged all the time. This is 

 probably due to the very smooth surface of the slide not retaining much 

 water. Likely the sporelings were exposed to more drought than they 

 could well resist. It was estimated that 25% of the sporelings became 

 detached from the slide. The sporelings receiving 3/^ light and no light 



