458 Dr. F. A. Bather— Prof. Nathorst's Studiea of Fossil Plants. 



or microspores cannot be decided, but at any rate the species is not 

 a Carpolithus. 



The structure of the sporangium itself can to some extent be made 

 out by following the gradual action of the reagents under the lens or 

 microscope. Besides the shape of the spore-sacs, one can see whether 

 the sporangium tissue consists of one or many layers. An illustration 

 of the method is provided by Nathorstia. Here the whole sorus forms 

 a firm, closed capsule. "When bleached with chlorate of potash and 

 nitric acid, it has at first the appearance of a quite homogeneous, 

 light-brown, discoid mass. When the action has proceeded further, 

 strong illumination under the microscope enables one to detect the 

 carbonised and still black septa between the groups of semi-transparent 

 brownish spores. These septa coalesce in the centre and taper out- 

 wards, so that they form a star. On the addition of ammonia the 

 sorus splits into wedge-shaped spore-groups. By pressing the cover- 

 glass on these, the spores are loosened. All these stages are shown by 

 microphotographs, of which the last represents most distinctly the 

 tetrahedral form of the spores under a magnification of 260 diameters. 



Not only ferns but other pteridophytes lend themselves to such 

 researches on the spores. The spores of Equisetites^ for instance, have 

 just been discovered in this way by Mr. Th. G. Halle (Sv. Yet.-Akad. 

 HandL, xliii, No. 1, 1908), and Professor Nathorst thus describes his 

 own discovery of two kinds of spores in Lepidostrohus Scotti : — Here 

 the sporangia are easily seen, and their thin wall is removed by Eau 

 de Javelle, which thus exposes the megaspores. This first treatment 

 further results in the recognition of their spore-nature, i.e. the 

 unicellular nature of the dark-brown objects can be determined, while 

 in some specimens one can also observe three ridges meeting at an 

 angle of 120°, as well as a peculiar appendage. One specimen showed 

 that this appendage was placed close upon the ridges, but this was 

 seen more clearly in another preparation which, after the first 

 bleaching with Eau de Javelle, was treated with alcohol and then 

 bleached further. These preparations are remarkably transparent and 

 allow the structure of the megaspores to be observed very exactly. 

 Once clear as to this structure, the next step was to find the 

 microspores, should such be present. The quest did not seem likely 

 to succeed, for very little carbonised matter remained, and none of this 

 was above the assemblage of megaspores. The only part suitable for 

 examination was further down, on the left side of the upper part of 

 the uncovered flower-axis, and seemed to correspond to three 

 sporophyll fragments with sporangia. This part, therefore, was 

 cautiously removed from the stone slab and treated with fuming nitric 

 acid. Since this, however, seemed too violent in its action, the 

 treatment was soon interrupted and Eau de Javelle substituted for the 

 acid. At the end of the bleaching, three closely compressed elongate 

 parts could be distinguished. One of them displayed a collection of 

 megaspores ; another resembled it ; both therefore corresponded to 

 two megasporangia. The third part, however, showed no megaspores, 

 but a perfectly homogeneous mass, on which there appeared here and 

 there circular spots of about 0*28 mm. diameter. Small isolated 

 fragments of the light brownish-yellow ground-mass were translucent 



