February 1, 1892.] 



KNOWLEDGE 



23 



capsules are of a firm, almost woody, structure, and give 

 to the whole plant a different character to that of most of 

 the Mosses. This peculiarity of the Polytrichum has, so 

 to speak, enabled it to play a greater part in the world 

 than most Mosses. Gilbert White tells us that the 

 foresters of his neighbourhood made " neat little besoms 

 from the stalks of the rolvtriclium, common or great 

 golden maiden hair, which they call silkwood, and find 

 plenty in the bogs. When this Moss is well combed and 

 dressed, and divested of its outer skin, it becomes of a 

 beautiful bright chestnut colour, and being soft and pliant 

 is verv proper for the dusting of bed curtains, carpets, 

 hangings, ic." But long before the dwellers in Wolmer 

 Forest discovered this use for this Moss, it had been 

 known to the pre-historic dwellers in our island, and 

 had, it appears, been used by them to adorn themselves or 

 their wives (themselves most likely). Curious fringe-like 

 objects plaited of the stems of this Moss have been dis- 

 covered in a crannog, or island fort, at Lochlee, in Ayrshire, 

 attributed to that pre-historic period which has been called 

 the late Celtic period. Furthermore, it is perhaps due to 

 this fibrous character of the class that the earliest Moss 

 of which we have any record in the strata of the earth 

 appears to be one of the Polytrichacefe. 



The roots or rhhoids of the Mosses are distinguished by 

 the minuteness of their growing ends, by their pliancy, and 

 by the presence on theu- exteriors of a balsamic or glutmous 

 deposit. To these points of structure they owe their 

 capacity to insinuate themselves into the minutest crences 

 of rock, to get, for instance, amongst the particles of the 

 oolites, and also to fix themselves in the shifting sands 

 of the sea-coast, and by so fixing themselves to give fixity 

 in return to the sand, and so tend to produce the sand- 

 dimes in many parts of the coast. At some parts of the 

 Northumbrian coast the Bncoiiiitriiiiii canesceiis may be 

 found buried deep in the sand, from which it can scarcely 

 be detached ; and in like manner the sand-dunes of Holland 

 and the west of France have in many places been fixed by 

 Mosses. The forests of firs on the North Sea and the Bay 

 of Biscay thus owe their place of abode to humble Mosses. 

 Leaves. — When we examine the" leaves of Mosses and 

 compare them with the more familiar forms presented to 

 us by the phanerogams, we find ourselves in a new world, 

 and the interest with which we view them is increased 

 when we remember that, according to the view usually 

 accepted, they are,' so to speak, a unique phenomenon ; 

 they are not the descendants of any earlier leaves nor the 

 ancestors of any later ones ; they appear thus once, as it 

 were, in the history of the vegetable kingdom, and advance 

 no further. They possess something of the charm which 

 an QTTa^ Xiyofieiiv exercises over the mind of a philologist. 

 We may first note what they are not. They are never 

 opposite, never whorled, never on leaf-stalks, never truly 

 veined, never lobed or compound, never furnished with 

 epidermis or stomata. 



When we turn 

 to consider afiSr- 

 mativel)' what 

 Moss leaves are, 

 we find them in 

 some cases char- 

 acterized byan ex- 

 treme simplicity 

 of form. They 

 are single plates 

 of similar cells 

 without midribs, 

 without veins, and 

 without border. 



The accompanying Fig. 18, representing a leaf of the 

 beautiful Moss, the Hookeria lucens, is an illustration of 

 this form of leaf, and the Figs. 19 and 20 will show more 



highly magnified the 



structure of the com- 

 ponent cells in a young 



and old leaf, and the 



grains of chlorophyll in 



the cells. In the old 



leaf a tendency will be 



observed in these grains 



to place themselves along 



the walls of the cells 



so as to produce the 



effect of thickened walls. 

 Mosses stand in im- 



of 



Fig. 19.— Cells of 

 young leaf of 

 Hookeria lucens, 

 after nature. — 

 A. F. 



The leaves 

 mediate connection with the atmosphere, 

 absorbing moisture from it when 

 moist, and shrinking and shrivelling 

 when the air is dry. In some cases 

 they are characterized by a marked 

 difference in the form of the cells 

 in the different parts of the leaf. 



Fio. 20. — Cells 

 of old leaf of 

 Hookeria lucens, 

 after nature.— 

 A. F. 



Fig. 18.- 



-Leaf of Hookeria lucens, magnified, 

 after nature. — A. F. 



and again in other cases by the imequal distribution of 

 chlorophyll ; in other cases we come across strange forms, 

 the like of which we hardly know in the phanerogams ; 

 such are the thick border and double rows of teeth in some 

 of the genus Mnium, the parallel plates in Polytrichum ; 

 and, stranger still, the third flange of the leaf inFissidens, 

 the true homology of which has proved a crux to bryologists. 



A drawing of the leaf of Fissidens adiantiuides is shown 

 in Fig. 21^a thickened line of cells down the middle of 

 the leaf assumes very much the appear- 

 ance of a midrib, and on the right hand 

 side occupying the lower half of the leaf 

 is seen a third flange to the leaf, attached 

 at its upper part to the leaf in an oblique 

 line and after that to the vein or midrib 

 of the leaf, so that in that part of the 

 leaf there are, as it were, two sheets or 

 plates instead of one. Various theories 

 of the homology of this part of the leaf 

 have been suggested. By some it has been 

 thought to result from a vertical splitting 

 of the leaf; but each of the two plates 

 where they ai-e doubled is of an equal 

 thickness to the rest of the leaf. Some 

 have suggested that the double portion 

 is alone the true leaf and the rest an 

 outgrowth, but this seems a violent 

 assumption. Others, again, have suggested 

 that the additional lobe is a stipule 

 arising on the opposite side of the stem, 

 which has become adnate with the leaf. 

 Some of these suggestions carry conviction 

 with them. 



In some cases the leaf is produced into a long thread or 

 beak, devoid of chlorophyll, and often with indented or 

 toothed edges. This structure is found chiefly in Mosses 

 living on stones and rocks, and in dry situations, such as 

 Grimmia and Eacomitrium, and the presence of these long 

 white threads or beaks gives a grey tmt to the whole Moss, 

 and in places where the Moss is predominant (as, for 

 instance, some parts of Dartmoor and North Wales, where 

 Eacomitrium abounds) a grey tint to the whole landscape. 

 These long hairs and prominences, especially when armed 

 with lateral teeth, no doubt retain the moisture which is 

 necessary not only for the vegetative life of the Moss, but 

 also for the process of reproduction by archegones and 



Fig. 21.— Leaf of 

 Fissidens adian- 

 fioides, showing 

 a a, the third 

 flange. After 

 Schimper. 



