86 THE VICTORIAN NATURALIST. 



plant, as in other Desmids, Chara, Nitella, &c. These may be 

 watched with interest under the microscope, and the still 

 uncertain causes of some of the latter class sought for by the 

 student as an aid in the solution of problems affecting higher 

 plants and possibly animals. 



Reference has already been made to epiphytal and epizoic 

 Algae, and it may be mentioned that many unicellular forms are 

 enslaved by species of Fungi which derive nourishment from 

 them by enclosing them within a meshwork of tubes, allowing 

 them to multiply by budding, in order to provide hosts for the 

 young Fungi produced at the same time. This combination of 

 Fungus and Alg?e is familiarly known under the name of Lichen. 

 Among the exhibits this evening a section may be seen where the 

 Lichen thallus has been cut through, exposing the green Algal 

 growth within the colourless meslnvork of tubes. 



Keeping in mind the delicate, perishable structure of these 

 plants as a whole, one would not expect to find traces of them 

 preserved in rocks, but there are representatives of at least two 

 families known to paleophytologists. The gyroliths or spiral 

 stones named by Lamarck, probably without his having been 

 aware of their vegetable origin, and which are to-day collected in 

 Europe, &c., and called Gyrogonites, are the hard pericarps of 

 plants allied to the Chara^and Nitella of the present time, which 

 a comparison of the drawings exhibited of the oogonium of a 

 living Chara, and that of the fossil C. medicaginnla and C. 

 grepini from the Paris basin, will show. The Diatoms, too, are 

 found in large quantities, as the free-swimming forms of these 

 plants exist in great numbers in salt and fresh water, and their 

 structure is such as to render them almost indestructible. The 

 Diatom has a shell or test, composed of silica, in two parts, one 

 of which fits over the other like the lid of a pill-box. When the 

 plants die these shells or frustules remain, and finally settle on 

 the bottom of ocean or lake to form a white sediment. Kerner 

 mentions a block of two cubic feet of Diatom-earth which is 

 preserved in the Natural History branch of the British Museum, 

 London. This block is composed entirely of Diatom shells 

 (twenty-one species being represented), and is computed to 

 contain over twelve billions of these minute forms. It is stated 

 to be from the bed of a fresh-water lake in Australia. Perhaps 

 geological members may be able to tell us more about it. Great 

 beds of fossil Diatoms, otherwise infusorial earth, exist in North 

 America and elsewhere in secondary, tertiary, and more recent 

 formations ; one in Virginia, U.S.A., is said to be some miles in 

 extent and forty feet deep. Among the exhibits may be seen 

 some Diatom-earth which looks like white chalk. The white 

 smudge on our fingers, if we handle it, consists of hundreds or 

 thousands of the minute plant shells, which may be seen also 



