54 



KNOWLEDGE 



[March 1, 1898. 



tbem, and the air shared ; but during this struggle, which 

 may last for weeks, the activity of the bacteria is impaired, 

 and though the conversion of alcohol into acetic acid still 

 proceeds, it does so with an increased expenditure of time 

 and a reduced yield. Should the vinegar eels gradually 

 obtain the upper hand, they interfere more and more with 

 the working of the apparatus, and eventually the conversion 

 of alcohol into acetic acid comes to a standstill. If, on the 

 other hand, the bacteria get the mastery, they form the 

 slimy layer, mentioned above, over the surface of the 

 liquid, as the result of their obtaining insufficient oxygen. 

 This skin effectually prevents the eels from breathing when 

 they come to the surface, and so they perish for want of 

 air, and fall to the bottom of the apparatus, where they 

 may accumulate and putrefy. In either case the only 

 remedy is to thoroughly clean and disinfect the apparatus 

 and commence afresh. 



It was only with great difficulty that Pasteur could 

 convince certain French vinegar manufacturers as to the 

 advantage of endeavouring to get rid of the vinegar eel, for 

 so general had it become with them that they had begun 

 to look upon it as an essential part of the process instead 

 of a deadly enemy. 



Even after vinegar containing eels has been freed from 

 them by filtration the germs remain, and when placed 

 under suitable conditions will develop into eels, which will 

 rapidly multiply and cause the vinegar to become turbid, 

 although it has been recently proved in (iermany that they 

 do not aiJect its strength. As Pasteur was the first to point 

 out the ill effects caused by the vinegar eel in the manu- 

 facture of vinegar, so, too, he was the first to devise an 

 effectual means of destroying them, with their germs and 

 all other forms of life in the finished product, by heating 

 it to about one hundred and sixty degrees Fahrenheit, 

 and then rapidly cooling it so as to prevent loss of the acid 

 by evaporation. And this is only one of the many instances 

 in which the studies of Pasteur on micro-organisms have 

 been of practical benefit to mankind. 



BOTANICAL STUDIES.-II. 

 COLEOCH^TE. 



By A. Vaughan Jennings, f.l.s., f.g.s. 



IN a preliminary study' we examined a common 

 fresh-water alga which showed in its simplest form 

 the process of oogamous reproduction ; the develop- 

 ment of a single egg-cell in a simple protective case, 

 fertilized by motile antherozoids formed in an 

 adjoining chamber growing out from the same plant- 

 filament. Apart from structural details of the plant in 

 question, attention was specially called to two points in 

 connection with its reproduction : firstly, that what might 

 be termed the "fruit" was only the fertilized egg-cell 

 surrounded by a thickened wall ; and, secondly, that on 

 germination this " fruit " (or oospore) grew at once into 

 a new plant, in all respects resembling the parent. 



Our next illustration may also be taken from the fresh- 

 water algip, and from a genus by no means uncommon in 

 this country, though not, perhaps, easy to find without 

 some careful observation. 



On the stems of water plants such as the water-lily and 

 the common pond-weed, or on the glass sides of aquaria, 

 may be found little green discs ranging in size from almost 

 invisible specks to circles a quarter of an inch or so in 

 diameter. 



* Vaucheria, KxowLEDGB, January, 1898. 



These belong to the genus Coleochmte* a well-defined 

 and widely distributed genus containing in this country 

 some three species. The plants are, it is true, very 

 frequently sterile, but the nature of the reproductive 

 process is of considerable importance in the line of study 

 we are following. 



It will be interesting, however, first to examine the 

 structure of the plant itself. If the species collected is, 

 as it most probably will be, either C. scutata or Corhkularit, 

 it will be noted that the whole plant is just a flat plate of 

 cells arranged in radial rows ; the cells all in one plane 

 and never superposed one above another. As the cells 

 have all a fairly uniform average size, this must mean that at 

 the growing margin many cells divide in two by radial 

 walls, and numerous instances of this will readily be found. 

 In another species — C. sohitu — the rows of cells are, in 

 fact, separated for a considerable portion of their length : 

 while in others, such as ' '. pulfinnta, the cells are no longer 

 in one plane, but grow up straight or obliquely, forming a 

 sort of cushion. 



In other words, we have within the genus t a series of 

 stages connecting the flat ceU-plate with the tree-like 

 growth of such types as BuUiochatt, one of the most 

 beautiful of our fresh-water alg». Among the red sea- 

 weeds, also, the early stages of some species of the 

 "coralline" Melulu'sia have a similar structure, and the 

 delicate discs of cells may often be found on the surface 

 of the larger weeds. A similar growth-type occurs also 

 on leaves in tropical countries, constituting the genus 

 Plii/C(tpeltis,\ but here a yellow colouring matter is present 

 as well ; and this fact, together with its reproductive 

 organs, shows it to be allied to the little yellow or red 

 filamentous algic of the genus ('hroiilepus (or TrenUpuMia) 

 which occur on rocks and trees all over the world. We 

 have, that is to say, similar or parallel types of growth in 

 plants which are otherwise widely separated. Some 

 writers seem to regard the disc type as derived from the 

 thread-like form ; but the early stages in development of 

 such forms as Phycoprltis seem, as I have elsewhere 

 suggested, i to point to an opposite conclusion. Theoretical 

 questions such as this are, however, outside our present 

 purpose. 



Coming to the question of the mode of reproduction in 

 ('ohochate, -we find, as in Vuticheria, th&t there are two 

 distinct methods. In the first case the protoplasm of some 

 of the cells of the thallus becomes contracted and rounded, 

 and finally escapes by an opening in the cell wall. When 

 liberated it appears as a free-swimming ^ovipmiilium with 

 a pair of long cilia. This, after a period of activity, loses 

 its cilia, settles down, and subsequently grows into a new 

 plant. The process is therefore physiologically similar to 

 the escape of the more complex :oin/o)iiilium of Vaticheria, 

 and has nothing to do with the formation of a true fruit. 

 It is again a case of " rejuvenescence " of a protoplasmic 

 particle without any combination with other elements. 



In the second case the contents of certain cells become 

 enlarged and specialized to form an orisphen, while some 

 of the other cells divide in four, and from each new cell 



* The name refers to the long bristle-like hairs ivitk a sheathing 

 base whicli occur on the cells of the disc in most species, but are 

 sometimes altogether absent. 



t The closely related genus Aphanochate, which also occurs on 

 ftesh-water weeds, shows in the same war an intennediate condition 

 between the discoid and the iilamentous growth. 



:J: The Mi/coidea parafitica (Cunningham), which causes disease 

 on the leaves of the coffee and other plants, is nearly related, but 

 may consist of more than one cell-layer, and may penetrate the 

 tissues of the leaf it grows on. 



§ Proceediigsofihe Boi/a' IrM Academy, 1895. 



