302 



SGIENGE. 



[N. S. Vol. XI. No. 269. 



clearly establish their relations to existing 

 types. So far as investigations have pro- 

 ceeded, we can now recognize a sporocarp 

 enclosing both macro- and micro-sporangia, 

 from which may be obtained the correspond- 

 ing spores with dimensions of 40 and 15 

 microns respectively. Prothalli in various 

 stages of development have also been ob- 

 tained. There is presumptive evidence 

 that the sporocarp may have been stalked 

 as in Marsilia, but the character of the con- 

 tents points more to an affinity with Pilu- 

 laria. The association of creeping rhizomes 

 strengthens the supposition that they were 

 aquatics of the general habit of growth of 

 Marsilia and Pilularia, while the recently 

 discovered occurrence of leaves of the 

 general type of Marsilia would seem to add 

 to the validity of this hypothesis. Although 

 closely and constantly associated in the 

 same beds, and even on the same slab, the 

 unfortunate separation of members will not 

 permit final conclusions as to the nature of 

 this plant at the present time. 



In 1885, the late Sir William Dawson 

 discovered in the Devonian sandstones of 

 Gaspe, the remains of a gigantic alga to 

 which he subsequently gave the name of 

 Nematophyton. This genus has since been 

 found to have a very wide distribution, 

 being found in Great Britain, Germany, 

 and various parts of the United States and 

 Canada as far west as Ohio. At present 

 eight species are distinguished, but it is 

 highly probable that with a more complete 

 knowledge of the plant, this number will 

 be greatly reduced, while the number of 

 genera may have to be increased. 



They were plants of arborescent habit, 

 •attaining a diameter of two feet or more 

 and a height which was undoubtedly great, 

 but which can only be conjectured from the 

 diameter and the fact that the largest speci- 

 men so far recovered from the Hamilton 

 Group of New York, although incomplete, 

 had a length of 24 feet. No foliage or fruit 



has yet been obtained, and our only guide 

 to relationship is through the character of 

 the internal structure. A pseudo-exogenous 

 structure, as in many Laminariese, is con- 

 spicuous. Isodiametric, radial or irregu- 

 larly branching openings occur in the 

 various species, and in these areas or in 

 their immediate neighborhood, the larger 

 cellular elements branch more or less freely 

 into small hyphse which form an intercel- 

 lular plexus. The principal elements of 

 structure consist of exceedingly long, non- 

 septate, thick-walled, tubular cells which 

 traverse the stem in the direction of the 

 longitudinal axis — though to a minor extent 

 transversely — and interlace freely to form a 

 medulla as in the larger forms of the Lami- 

 nariese. No surface markings of the walls 

 have been observed, but in one species (iV. 

 Ortoni) the cells show local enlargements 

 closely resembling the trumpet hyphse of 

 Macrocystis. 



One of the most instructive features of 

 these plants is to be found in certain struc- 

 tural modifications which they exhibit. In 

 working up material from various sources, 

 it was discovered that many specimens ex- 

 hibited certain transitional forms from nor- 

 mal structure to what was described many 

 years since by the late Sir William Dawson 

 under the name of Celluloxylon primcevum. A 

 closer study revealed the fact that this al- 

 teration was incident to the crystallization 

 of the infiltrated silica and the operation of 

 decay, whereby the carbon particles of the 

 original cell walls were redistributed upon 

 the surfaces of the crystals in such a manner 

 as to produce the general effect of a coarse 

 cellular structure. 



Notes on the morphology and reproduction of 



Chlorocystis Cohnii : Me. G. T. Mooee, 



Dartmouth College. (Bj' invitation.) 



The structure and development of this 



unicellular alga growing on Entromorpha 



was described and several points differing 



