8 Brannon, — The Structure and Development of 



While direct sunlight appears necessary for the continued 

 growth of the plant, it cannot endure strong light when only 

 slightly submerged. If after collection the plants are placed 

 in water in a shallow vessel, exposed to the direct rays of the 

 sun, their normal colour rapidly changes to a brownish yellow, 

 and they give every evidence of rapid decay, evidently due to 

 the effect of direct sunlight and the accompanying rise of 

 temperature. Direct experiments were not made to deter- 

 mine the sensitiveness of Grinnellia to changes of temperature 

 alone, but incidentally it was observed that a sudden variation 

 of io° to 15° C. from normal (temperature of 15° C. in the 

 water of Vineyard Sound) for any length of time is destructive 

 to the tissue. Fishermen reported collections of this plant in 

 the winter. Having cut through the ice they could scrape 

 it from the piles, in water of which the temperature was 

 probably not lower than a° to 5° C, while in the summer the 

 temperature of these waters, as previously stated, is 15° to 

 17° C. 



The three types of fronds, antheridial, carposporic, and 

 tetrasporic, show a similar degree of sensitiveness to direct 

 light and sudden rise of temperature, but can be preserved in 

 a normal condition for several days in the laboratory if 

 properly shaded, if the normal temperature of the containing 

 water be maintained, and if the sea-water be changed every 

 thirty-six to forty-eight hours. 



Nowhere are the effects produced by the change of light 

 and temperature more perfectly shown than in the process of 

 sporing and germination. The spores are liberated in great 

 numbers during the night, particularly the second night after 

 the plants are collected. However, numerous experiments 

 proved that this process occurs in some degree during the 

 day, differing in this respect from the sporing methods 

 observed in some other Florideae, notably Champia parvula. 



Immediately after collection, the carposporic and tetra- 

 sporic plants were separated in order to study the germination 

 of their respective spores. It was found that the carpospores 

 are usually closely grouped in great numbers immediately 



