ON THE ZOOLOGICAL STATION AT NAPLES. 81 



and with that of the main stem ; the branches are developed as hollow- 

 processes of the mother cell, and these constrictions are formed by thicken- 

 ing of the cell-wall at the points branching, but the lumen does not close 

 during life, though it is reduced to a very narrow opening. When the 

 stem of a vigorous plant is cut, the contents flow out of the opening, and 

 the protoplasm contained in the basal branches of the hairs can be observed 

 to flow into the stem, while in the smaller hairs the contents, so to speak, 

 endeavour to do so, collecting at the base of the branch, but not being able 

 to pass through on account of the constriction. When the hairs die off, 

 the smaller hairs die first, the contents apparently passing down into the 

 cell below, and a membrane being formed across the opening, and so on 

 down to the basal cell. I have only observed this in the case of the basal 

 cells, but I conclude that it applies to the others, for the basal cells at this 

 time are crammed full of protoplasm and other cell-contents, so that they 

 are almost opaque, while their minor branches have disappeared. The 

 membrane formed across the opening into the stem is thin at first, but 

 becomes thicker by the deposit of layers of cellulose. The hairs appear 

 to be analogous to the branches of the West Indian BhijyocephaJus and 

 Corallocejyhalus. Their function I could not determine ; they contain a 

 small amount of chlorophyll and the red oil found in the chlorophyll 

 bodies, but too little to be of much use, except perhaps in the basal 

 branches. Perhaps they are reduced organs ; it is conceivable that at one 

 time they may have been important organs of assimilation, as the branches 

 of the West Indian forms mentioned are still, and that their function may 

 have been taken from them by the greater development of the pileus. 



I also investigated the mode of formation of the pileus. The cell- 

 wall at the end of the stem is very thick just before it begins to be formed. 

 The inner layers of cellulose appear to be absorbed at definite points, 

 while the outer ones are pushed out, the cell being intensely turgid at this 

 time, and form the walls of the branches. There is no organic connection 

 between the branches ; at their bases they are distinct, and when decal- 

 cified the branches can be readily separated from one another; in the 

 slightly calcified A. crenulata of the West Indies they are often separate 

 during life. The branches of the pileus would appear to be more or less 

 homologous with the hairs. 



I also made some experiments on the brown ethereal oil found in the 

 chlorophyll bodies of the majority of joung Acetabularia, which it colours 

 a rich red brown, and even in many full-blown ones. I could find no 

 starch in the brown specimens, while there was a good d' al in the green 

 ones, and I thought it possible that the oil might be a product of assimi- 

 lation, especially as some species of Vaucheria, Musa, and other plants are 

 said to contain oil instead of starch. My experiments gave no result, posi- 

 tive or negative; partly, at any rate, owing to the difliculty of keeping 

 Acetabularia alive in an aquarium. There seems, however, to be a pre- 

 sumption in favour of the theory that the oil is a product of assimilation. 



I hope, in the autumn, to be able to make some observations on the 

 sinking of the cell-contents into the basal part of the stem, the death of 

 the upper parts, and the condition of the plant during the winter. 



One of the main objects of my coming to Naples was the study of the 

 SipJwnece, and especially Caiilerpa. I have studied in addition to Acetabu- 

 laria and Gaulerpa, the genera Codium, Valonia, Udotea, Bnjopsis, and 

 Dasycladus. My results with Gaulerpa are perhaps worth stating, though 

 they are by no means complete. As a means of inducing the plant to 



1887. Q 



