the species. Under each species he gives the measurements both of the length and breadth of these 

 cells and founds on these grounds a new species and a new variety. 



The most important point in Professor Askenasy's account of Halimeda is his descrip- 

 tion of the central strand of filaments. He shews that not only do these filaments run up like 

 a midrib through the centre of the plant, but that all further growth originates in the first 

 instance from them and that they approach each other at the top of each joint and grow together. 

 He says : "Here their membrane becomes much thickened in places, whereby the connection is 

 still more strengthened , while at the same time large circular or elliptical holes or pits are 

 formeel in a definite narrow zone , by means of which the contents of the tubes are placed in 

 quite free communication with each other. Each tube has at the node several such holes and 

 two or more tubes can communicate with each other through several holes". 



He illustrates this by figures of the node of H. incrassata. Professor Askenasy then 

 goes on to describe the apex, where these pits are originally formed : "One sees then the 

 central filaments running in a thick bundie to the apex and at the apex itself growing together 

 for a short distance. Here are now formed the holes, which were mentioned above. Seen from above, 

 the ends of the filaments of the central strand form an irregularly bordered group ; they are to be 

 distinguished at the first glance from the neighbouring peripheral cells by their considerable size". 



The account given by Professor Askenasy of the growth which takes place to form a 

 new joint is not in all respects in accordance with my observations, which are given under 

 'Tnternal Structure" on p. 5 below. 



The result of an examination of the calcification in Halimeda is also given in this paper 

 and as nothing further has been added to our knowledge in this respect, Prof. Askenasy's results 

 are quoted at length under the heading of Calcification below. 



Our knowledge of the genus Halimeda was in this position when, by the kindness of 

 Prof. Judd, the Funafuti collection of Halimeda was placed in my hands for identification and 

 examination : and a year later, unfortunately after the publication of the Funafuti results, Mad me 

 YVeber — van Bosse was so kind as to entrust to me the working out of her largfe collection 

 of this genus made by the Siboga-Expedition in the Dutch East Indies in 1S99 and 1900. 



This collection, together with the specimens of this genus in the British Museum and 

 Kew Herbaria, and other collections which have with great kindness been lent me for compa- 

 rison, have formed a sufficiently large series to allow of an attempt being made to delimit the 

 species; with the result set forth below. 



Morphological. 



External form. Halimeda is composed of a series of calcified joints, connected end to 

 end like the beads of a chain and branching di-, tri- or polychotomously. The individual plants 

 vary in length up to about 40 cm. and may be prostrate, sparingly branched and straggling, 

 or erect, much branched and forming a close short tuft. Between these two extremes is 

 a large range of variety, probably dependent to a certain extent on depth and movement 

 of the water. So far as I know, there are 110 records from collectors as to the effect of such 



