188 



" Alga: Britannicse," yet his examination was unsatisfactory, as he could detect 

 no fructification, and says the vesicle is "filled with a watery fluid, which 

 escapes by an irregular terminal orifice." This is not the case, as no orifice 

 could be detected either by myself or my friend Dr. Holl, who has carefully ob- 

 served the plant under his microscope ; and though a little moisture occasionally 

 exudes when the vesicle is crushed, yet it seems really to be inflated with air, 

 which may readily escape without a terminal orifice ; and, in fact, a continuous 

 cavity runs through the entire plant. 



Having had the plant under notice for several years, I think that I am 

 now familiar with its structure and economy, though to understand the former 

 requires a very careful eye. From its peculiar position, it is difficult to catch it 

 in its first state, when the whole plant is invested with a thin pellicle or swaddling 

 cloth, so to speak, forming several membranes or lamellae, which it bursts 

 through, and then appears as a polished green globule, mostly scattered over 

 with granular specks on the surface, which are the relics of the thin mem- 

 branes it has burst through. This second globular form does not last long— 

 a day or two at the utmost — when the globules quietly collapse, and, form- 

 ing a junction with each other, an extended green frond or crust presents itself, 

 appearing very much like an Ulva, and which may exist, if the mud on which it 

 is fixed remains moist, a considerable or unlimited time ; but under the influ- 

 ence of the sun it soon withers up into a white efflorescence. 



The vesicles are often crowded together in little tumps, like cushions, 

 made up of innumerable globular vesicles, so minute as scarcely to be visible to 

 the naked eye, and these appear to be proliferous masses attached to one branch- 

 ing root. "When examined under the microscope, the vesicles are seen to collapse 

 in a very curious way, each vesicle sinking into a concavity without any rupture 

 of the epidermis of the vesicle, the moisture within, if any, sinking through 

 the funnel-like tube below. This collapse of the vesicle goes on rapidly, yet 

 almost imperceptibly, until the globules have all disappeared, and only an ex- 

 tended green frond appears to view, which is the last state of the Botrydium. 



The collapse of the vesicle seems to be a mere desiccation, for there is no 

 aperture for the escape of moisture, and the collapse places the vesicles in their 

 secondary vlvoid state, when by their junction they form a frond, differing 

 much in appearance from their original grape-like aspect. 



The vesicle appears to consist of two transparent membranes, between 

 which is a mass of granular matter bearing some resemblance to a Chlorococcus, 

 but with frequently only a single granule in a cell. These cells are very nume- 

 rous, and, in the breaking up of the vesicle, may sometimes be seen to spread 

 out in a flowing stream under the microscope, but generally they remain in- 

 active. 



The vesicles are attached to the mud in which they grow by long divided 

 threads or roots, and in general these threads support but one vesicle ; but 

 where bosses of very crowded minute vesicles present themselves to view, as 



