4 GEAF ZU SOLMS-LAUBA.CH— MONOGRAPH OF THE ACETABULAEIE^. 



homogeneous cliloropliyll-l3earing protoplasmic layer of the sporangial ray small, 

 completely colourless, round spots, about which the protoplasm gathers as about 

 attraction centres. De Bary, who cites tbese spots, says (9, p. 719) " eacb spot appears 

 to be a centre of attraction for a portion of the protoplasm, and may therefore well 

 correspond to a nucleus." This appears to me to rest on a misunderstanding of 

 Woronin's statement. Since, as his drawings show, these clear spots remain con- 

 tinuously well defined up to the complete rounding off of the spores, they cannot 

 well be in the centre, but must rather be towards the outside of the young spores 

 (compare "Woronin's figures, pi. 6. figs. 1-5) ; in figs. 1 and 5 there is at the periphery of 

 the primordial spore a shallow excavation, and Woronin says expressly '* en examinant 

 plus attentivement la structure de ces corps elliptiques on voit qu'ils ne consistent qu'en 

 un sac primordial, qui a a sa surface une petite cavite, ou, ce qui est memo probable, una 

 ouverture." There can scarcely remain any doubt that this cavity represents the profile 

 view of the clear spot, the filling up of which with colourless protoplasm the author had 

 not sufiiciently taken into account, although he has drawn it in fig. 4 in the form of an 

 outline running over the excavation. Should it indeed be so, then the point ought to be 

 farther enquired into whether the clear spot contains a nucleus, or whether these are to 

 be found in numbers distributed throughout the protoplasm, as a priori appears more 

 probable. We know from Schmitz's investigations that in the chambers of the disc of 

 sterile plants of Acetabularia there are present, together with numerous small chloro- 

 phyll bodies, a large number of very small nuclei, which are much smaller than the 

 chlorophyll grains among which they are irregularly distributed. He then continues : — 

 "In the formation of the spores and zoospores there have been repeatedly observed, as 

 is knoT\Ti, clear spots which doubtless represent nuclei. Their size, however, is far more 

 considerable than that of the very small nuclei in the cap of the sterile plant, and their 

 number much less. There must take place before spore-formation various processes in 

 connection with the nuclei of these plants, perhaps conjugations like those recently 

 described by Berthold for JDerbesia'' He takes accordingly precisely the position of 

 de Bary in his interpretation of the clear spots. 



I believe I have seen these minute nuclei in the protoplasm of the stalks of 

 preserved material of A. mediterranean and would even assume that they are to be 

 found in the layer next the wall of the spores among the amylum granules; but I 

 certainly cannot express myself on this point with complete definiteness because I could 

 not, among the many difficulties presented by this plant, succeed in obtaining an 

 undoubted nuclear stain with any staining agent. 



Wliile I must thus leave the whole question of the nucleus and its elucidation to 

 future observers, I should like to call attention to the possibility of explaining the whole 

 body of facts in the following way. The peripheral clear spot of W^oronin's figures 

 recalls in a striking manner the colourless protoplasmic portion which bears the cilia of 

 an ordinary Confervaceous zoospore. If one now assumes that there is here a true homo- 

 logy, then the cap would correspond to a true zoosporangium of which the zoospores no 

 longer develop cilia and do not escape, but rather surround themselves with a membrane 

 at the place of origin, and enter at once into a resting stage, as indeed happens elsewhere 



