AND GERMINATION OF ALGiE. 71 



mediate transformation of the " cutaneous layer " (of the 

 so-termed "primordial utricle"). The separation of a por- 

 tion of the " cutaneous layer," as above described, renders it 

 certain that, at the time when the rostrum of the sporangium 

 is ruptured, the contents of the latter are not surrounded by any 

 proper membrane : but it is also obvious that the cutaneous 

 layer, which after the escape of a portion of it through the 

 opening still surrounds the green contents of the sporangium, 

 and is accumulated in a particularly thick stratum over that 

 part of the contents which correspond with the opening, 

 diminishes considerably in thickness when the formation of 

 the membrane ensuing upon the impregnation takes place ; 

 and this diminution in thickness goes on in proportion as the 

 membrane in question increases in thickness (figs. 10, 11, 12, 

 13). In this case the transformation of the cutaneous layer 

 into the membrane may almost be witnessed. This membrane 

 gradually increases to a considerable thickness ; at a later 

 period it appears to be formed of numerous tliin lamina?, and 

 it applies itself to all parts of the open tunic of the sporan- 

 gium (fig. 14). After the completion of the coat of the true 

 spore, scarcely a trace of the previously well-developed cuta- 

 neous layer remains ; an excessively thin parietal lining con- 

 stituted of it alone remaining. The green contents, which 

 had been forced back by the accumulation of the cutaneous 

 layer, in the mean while again spread themselves uniformly 

 throughout the perfect spore, and form as in all cells a thick, 

 internal parietal coating. 



The true spore thus formed by the impregnation represents, 

 consequently, a large cell occupying the whole of the sjwran- 

 gium, whose membrane, formed probably in consequence of and 

 certainly after the impregnation, appears to be laminated. 

 It is surrounded on all sides by the persistent tunic of the 

 sporangium, which is open in front and prolonged into the 

 rostrum. 



In this condition the spore remains for some time longer, 

 without being thrown off fi'om the parent tube on which it 

 was produced : but the colour of its contents, which was at 

 first green, gradually becomes paler and paler ; the spore is 

 at last I'cndered quite colourless, and presents in its interior 

 only one or more largish dark-brown bodies (fig. 14, 16). 

 When it has lost all its colour it is detached from the parent 

 tube, in consequence of the decay of the membrane of the 

 sporangium enclosing it (fig. 17). After some time (in my 

 experiments, after about three months) the spore, which is 

 readily recognizable by the red-brown miclei in its interior, 

 suddenly resumes its green colour (fig. 18), and immediately 



