SCIENCE-GOSSIP. 



303 



MICROSCOPIC ALG^. 

 By James Burton. 



{Contiiined from page 271.) 



"DEFORE going further it is necessary to explain 

 that by Lyngbya is here meant the plant 

 which Dr. Cooke, in his " British Freshwater 

 Algae," p. 182, names Ulothrix radicans (or 

 parietina, for the difference is very slight), and not 

 that now correctly understood under the name of 

 Lyngbya, which belongs to a much lower group — 

 the blue-green Oscillatorieas. 



Lyngbya muralis is an older name for the species 

 intended, and has a convenience for use in this 

 instance, as it is employed in all but the most 

 modern books of reference. I shall take the liberty 

 of adhering to it for that reason. The name occurs 

 in " One Thousand Objects for the Microscope " 

 (paragraph 472), and is apparently applied in the 

 old sense, though the description is scarcely definite, 

 but figs. 21 and 24, plate vi., stand for species 

 of the same genus, Ulothrix, and may be taken 

 to represent our example, for it varies very 

 considerably in size and other characteristics, 

 according to its circumstances and condition. It 

 consists of unbranched filaments, composed of 

 cells usually much broader than long, the outer 

 wall of the row being thick, sometimes swelling 

 in water till it is very thick and gelatinous. 

 The colour is the distinct green of chlorophyll, 

 an important distinction. In comparatively dry 

 situations I believe propagation takes place solely 

 vegetatively, by portions of the thread, or sometimes 

 single cells only, becoming detached and developing 

 into new filaments ; but in water, certainly in some 

 species and most probably in this, other methods 

 occur. In non-sexnal reproduction the protoplasm 

 of some of the cells is formed into from one to 

 eight pear-shaped bodies (zoospores) furnished at 

 one end with four cilia, by means of which they 

 move through the water for a time, finally attaching 

 themselves to a suitable object, and growing up 

 into a new plant. There is also a primitive kind 

 of sexual reproduction. In it the protoplasm 

 divides into a larger number of zoospores, each 

 with two cilia ; these swim about actively, and if 

 two, originated in different cells, come in contact, 

 they gradually unite and form one large zygospore. 

 This comes to rest, attaches itself, and slowly 

 grows. After a time a number of zoospores are 

 formed in its interior, which, when set free, no 

 doubt develop into fresh filaments, though this 

 does not yet appear to have been actually observed . (i) 



Lyngbya is even more widely distributed than 

 Piasiola, and may be found not only on the ground, 



(1) Vide Dr. Scott's " An Introduction to Structural Botany,' 

 Part ii. 



but on trees, posts, etc., and as its specific name — 

 muralis — implies, seems especially prevalent on 

 damp walls, even hanging like a green fringe 

 from projecting corners and edges of the bricks. 

 It is able to bear desiccation without injury, but 

 flourishes luxuriantly when well supplied with 

 water. For observation it may be cultivated in a 

 saucer on a little earth, or on the pieces of wood or 

 brick on which it may be found. Owing to the 

 wet weather of last February, there is no difficulty 

 in finding it at present in any quantity. 



Between the filamentous Lyngbya and the expanded 

 membrane-like Prasiola there is another form of 

 alga found in the same situations, partaking to 

 some extent of the characters of both ; this has been 

 named Schizogonium, and, as was mentioned last 

 month, has been classified as a genus of the Ulvacese. 

 It is figured in Dr. Carpenter's " The Microscope " 

 (sixth edition, p. 294), and also in the seventh 

 edition, as Ulva, and the same figure is given in 

 the " Micrographic Dictionary " (third edition) 

 as Schizogonium. The definitions are not very 

 satisfactory, and the plant itself, as far as it is 

 possible to identify it, varies extremely. " British 

 Freshwater Algas " gives: " Threads as in Ulothrix ; 

 or, in many places, laterally connate (duplicate or 

 triplicate), or by cellular division in two directions, 

 forming narrow, flat bands, which are more or less 

 crispate." 



To me, and probably to most students, the 

 greatest interest about these plants is in connection 

 with the statement that the filamentous Lyngbya 

 will, by division of its cells in a longitudinal direc- 

 tion, develop inio Schizogonium, described above, 

 and that this, by continuing the process and 

 increasing only laterally, at last reaches the 

 condition of a membranous frond and then is 

 the actual organism known to us already as 

 Prasiola. 



Dr. Braxton Hicks, in a paper in the " Quarterly 

 Journal of Microscopical Science " for 1S61, pp. 157- 

 166, says: "The only real difference between the 

 first two is that whereas Lyngbya is a tube contain- 

 ing distinct cells within, which, when old, undergo 

 collateral division to form a band of two, four, or 

 eight rows of cells, Schizogonium is a band of two 

 or eight rows of cells, which, when young, was but a 

 single row contained in a tube ; which is only two 

 different ways of stating the same facts. The 

 comparison of the last two is of the same 

 kind. For as Prasiola, when old, is composed 

 of many rows of cells, but which arose from 

 a single row, there must have been a time in 

 its life when it had two, four or eight rows, 

 and thus have been a Schizogonium, for there 

 is no other structural difference between the 



