Spore-For7natio7i of MesocarpecB. 43 



interrupted by the brass plate. By placing the eye at the hole 

 F, and looking at a suitable object upon the stage of the 

 microscope, a most wonderful sight will be seen. The object 

 will be brilliantly shown upon a dark field. I would suggest 

 its trial upon the diatom Heliopelta. It is not necessary to 

 explain the principle of the device, as it will be quite evident 

 to those familiar with optical work. By revolving the eye 

 piece in the body tube many curious changes in the appear- 

 ance of the object will take place. In using oblique light it 

 will be found best to place the hole on the opposite side of the 

 cone of rays from the mirror. The arrangement can be used 

 with the common eye piece, but with an inferior result. The 

 value of the device can be tested by making a hole in card- 

 board with a small pin, and holding it at its proper place over 

 the eye piece. 



Ottumwa, la., Sept. 2, 1878. 



[The principle involved in the above may not be seen at once by all our readers. 

 A little thought will show that the object is not seen by transmitted light, but by 

 that which it radiates itself ; the direct light from the mirror being quite cut 

 off.— Ed.] 



— ^ 



ON THE SPORE-FORMATION OF THE MESOCARPE^. 



A paper on this subject was presented by Dr. Wittrock 

 before the Swedish Academy of Science last December and 

 published in the Bihang till k. Sveiiska Vet. Akad. Handlingar, 

 Band V. The publication is not accessible, so we cannot refer 

 to the original (which is printed in English), but as the views 

 advanced by the writer are worthy of more than a passing 

 notice we do not hesitate to reprint the following from N'ature. 



In one lovely group of green-colored algse we find a number of very 

 pretty species, many of which consist of one-celled forms, and others 

 of which, obeying a law of cell growth, not only produce new cells but 

 also cause these to adhere to one another and so, as this growth goes 

 on, give a chain-like or filamentous appearance to the mass. These 

 filamentous green freshwater algae are very common. Dillwyn, in the 

 beginning of this century, knew and described many of them, and he 

 also seems to have well known that the contents of some of their cells 

 formed oval bodies called resting spores. The merit of having worked 

 out the history of these spores belongs to Prof. A. de Bary, from whose 

 researches it was first made clear that in some of these forms 

 (Zygnema) one of the chains of cells will come to lie alongside of an- 

 other chain, and then the cell-wall of two opposite cells will grow out- 



