SCIEXCE-GOSSIP. 



MICROSCOPIC ALG-E. 



Bv James Burtcn. 



T T would be difficult to suggest any more beautiful 

 objects for examination under the microscope, 

 and certainly none are easier to obtain than the 

 common species of lower algae. Owing to the wet 

 and mild weather we have been having, thej- are to 

 be found everywhere : on old walls, fences, and 

 tree-trunts, and on the ground at the base of these 

 thev are abundant. The dweller in to^\-□, as v.ell as 

 his more fortunate country confr'ire, has them plenti- 

 fullv at hand. "V'Miile all are interesting and may be 

 easily investigated by even the beginner, identifica- 

 tion is often sufficiently difficult to seriously engage 

 the attention of those weU practised in ordinary 

 botanical work. Unfortunately there is no exactly 

 popidar work dealing with this class, and the more 

 technical books are expensive and go further into 

 the subject than an amateur would care to do. 

 Still much may be accomplished by a diligent use 

 of small means. Dr. Cooke's little book, " One 

 Thousand Objects for the Microscope," published 

 at one shilling, contains a brief but useful 

 description and some illustrations of many species. 

 Indeed, this book forms quite a vadi mecum in ever>- 

 department for the play-time microscopist. The 

 plant now to be considered does not appear in it 

 by the name given here, but, as will presently be 

 seen, is not entirely unnoticed. 



Pr.^siola is perhaps one of the most common 

 and it is certainly not the least interesting of the 

 terrestrial algae, if one may be allowed to use a 

 term which is more descriptive than logical. It is 

 found in somewhat sheltered situations on the 

 ground, at the base of walls, fences, etc. "Within 

 a short walk of my neighbourhood there are more 

 than half-a-dozen places where it flourishes all the 

 year round, and may be foimd in greater or less 

 abundance, according to the weather. It con- 

 sists of a bright green, very thin membranous 

 frond, var^-ing considerably in size ; a nice specimen 

 I carefully spread out lately — no easy matter — was 

 about three-quarters of an inch long by half an 

 inch wide. The frond is much folded and 

 crumpled, v,-ith the edges often lobed, and tinder 

 favourable conditions growing \dgorously, and 

 producing short filaments and proliferations. 

 Under the microscope the plant is seen to be 

 composed of square cells filled with green proto- 

 plasm, w-ithout a nucleus ; the walls are somev.-hat 

 thick. The layer of cells is one deep only; they 

 fit closely together, and are arranged sometimes 

 in lines but more frequently in squarish areas, 

 bounded by walls somewhat thicker than those 

 between the indi\-idual cells. The whole forms a 

 pretty object when nicely displayed, and has been 



compared by an old wxiter to a well laid out 

 garden, with walks between neatly- disposed flower- 

 beds. A half or quarter inch objective is neces- 

 sary for the details. 



Prasiola is a member of the order Ulvaceae, to 

 which belongs the very common and well-known 

 seaweed, Ulva, sometimes called sea-lettuce or laver, 

 and in Ireland, sloke. This is plentiful on most 

 shores, and closely resembles a gigantic Prasiola, 

 consisting of membranous fronds often many 

 inches in length ; but ha\dng two layers of cells 

 instead of one only it is thicker and tougher. 

 Enteromorpha is another genus in the same 

 order, its frond is tubular and floats in either 

 fresh, brackish or salt water, according to 

 species. A plant called Schizogonium is usually 

 reckoned as another genus, and will be referred 

 to presently. 



One of the most interesting facts about Prasiola 

 is its persistent vitality under unfavourable con- 

 ditions. Though delighting in moisture, it bears 

 desiccation without injur5% and during the two last 

 dry summers has been found in the usual places, 

 perfectly dry and ready to break up vnth. a touch ; 

 yet on being placed in a saucer of -water it at once 

 absorbs moisture and becomes pliant, the green 

 colour revi\-es, and it is read}- to start growth with 

 renewed %"igour. Specimens treated in this way smd 

 then left to dr}- up have revived again and again, 

 though on some occasions left in the desiccated 

 state, and even in the sun, for weeks at a time. 

 Though so tolerant of drought it is not soon 

 injured by what would seem an equad excess in the 

 other direction, and it flourishes well and 

 apparently indefinitely if kept actually in water. 

 It grows qtute freely in an aquarium, though 

 generally suffering from the attacks of the 

 various aquatic animals which feed on it readily. 

 Even the extremes above referred to do not 

 e.xhaust its adaptive capacities, for it will endure 

 a not inconsiderable amount of salt in tte 

 water it is growing in, and, I believe — though 

 not speaking from experience — it is sometimes 

 found in brackish marshes. Of course freezing 

 is a matter of indifference to such a plant, 

 and it recovers from the process without difficulty. 

 There is one thing, however, it does not seem 

 capable of enduring, and that is being overgrown 

 by grass and other small herbage. At the beginning 

 of the wet weather w^e had last autumn there was 

 a fine patch close to a fence in this district, but as 

 the wet weather continued the grass, which the 

 previous drought had destro}-ed, began to grow 

 among the Prasiola, and a httle later, on going to 



