14 



distinctly separated from the outer at the base, leaving a 

 small chamber between the plug-like septum and itself 

 (compare fig. 20, PI. III.). Similarly, at the apex of the 

 sporangium, a like chamber is formed, and the inner wall 

 itself, as shown in fig. 16, swells and exhibits very definite 

 lamellation. The occurrence of these cavities at the base 

 and apex of the sporangium was obviously noted both by 

 Derbes and Solier and by Harvey, for their figures of the 

 sporangium illustrate, though somewhat roughly, the 

 peculiarity to which we draw attention. The sporangial 

 cavity is from half to three quarters full of a dark green 

 mass which, on careful focussing, is seen to be composed 

 of spherical bodies, each crammed with chloroplasts. 



Notwithstanding the fact that we examined hundreds 

 of sporangia for long periods, and extending over three 

 months, only once were we so fortunate as to see the zoo- 

 spores escape. As described by Derbes and Solier, they 

 escaped en masse, the apex of the sporangium rupturing 

 suddenly, probably owing to pressure exerted from within 

 by the swollen inner layer of the sporangium wall. The 

 green mass gradually dissolved in the sea-water (in which, 

 of course, the observations were made), and individual zoo- 

 spores freed themselves and swam off. The zoospores were 

 dark green, with a clear apex, and showed, in the apical 

 region, a body which was doubtless the nucleus described 

 by Berthold. Each w^as provided with two ciha. We 

 were unable to keep the zoospores alive until germination 

 had ensued, though we purpose repeating our observa- 

 tions in the hope of solving the question as to whether 

 they are zoospores or gametes, as Berthold believes. 



The s[u)i-anginiu is, early in its development, isolated 

 from (he i)alisade cell by an annular thickening in its 

 narrow pedicel (PI. IIF., fig. 20). This thickening becomes 

 finally a complete plug, and after the contents of the 



