Jdly 1, 1898.] 



KNOWLEDGE 



163 



BOTANICAL STUDIES.-IV. 



MNIUM. 



By A. Vaughan Jenninos, f.l.s., i'.g.s. 



IN our last study '■'■'■ we examined the reproductive 

 process and life history of a .lunin'imannia as a type 

 of the lower mosslike plants which are grouped 

 together under the name of Ilepatiae or Liteniurta. 

 It was observed that in these forms — among the 

 lowest of truly terrestrial plants — the oosp/ieirs or egg-cells 

 are contained in special flask-shaped structures or an-ln- 

 ijonia : that the fertilized egg-cell gives rise to a sporophyte 

 consisting of a globular spm-e nm,- or cup.iuh , borne on a 

 colourless stalk or st'ta which has its base embedded in the 

 tissues of the parent shoot ; that the whole contents of the 

 capsule break up into spores and elastic filaments (i-loter^), 

 which are liberated by the bursting of the capsule wall 

 into four segments ; and that the germination of these 

 spores produces a more or less developed cell filament 

 (protonema), from which buds a new Jun<iermiinnia plant to 

 bear when mature the reproductive organs in its turn. It 

 is now proposed to compare with this story the life cycle of 

 one of the true mosses. 



We may safely start with the statement that the life 

 history of a moss resembles in its main features that of a 

 Liverwort, though there are important differences in detail. 

 In selecting a type for study one looks for a form that is 

 at once abundant and widely distributed, easy to recognize, 

 habitually fertile, and large enough for easy manipulation. 

 The genus Mniiiin is less universally obtainable than 

 Funoriii or Poh/tiicJium, but it combines a typical sporo- 

 phyte borne on a leaf-bearing plant which is at once 

 conspicuous, beautiful, and easy of study, even with a lens 

 and knife if a microscope is not at hand. It is one of the 

 forms with hanging bell-like capsules, and was formerly 

 included in the wide generic type Bri/um. The species of 

 Mniuiii have stems from one to three inches in height, and 

 broad, dark green, large-celled leaves. They may be found 

 on wet banks in woods, and especially in the shady hollows 

 among the rocks of our mountain districts. Taking any 

 of the species, we may start our story, not with the anatomy 

 of the plant, but with the single cell from which the plant 

 has arisen. 



M. punctatum is perhaps the commonest and best for 

 study. It has large, wide, entire leaves, blunt at the tip; 

 while M. hornuiii has the leaves longer, narrower, pointed, 

 and toothed at the margin. M. latdidatiini (Neck) is the 

 largest and most beautiful species, with long, narrow, wavy 

 leaves, but is only rarely fertile. The specimens used for 

 this article were collected in Switzerland in May last, and 

 I am not sure of the exact species. Probably the first 

 (E and F) is a small-leaved variety of M. honium .- the 

 other seems nearest to M. aiiine (Schwaeg). The question 

 of species is, however, of no importance for our present 

 purpose. 



When the moss spore falls on a suitable spot under 

 conditions favourable for germination, its protoplasmic 

 contents, covered by the delicate inner spore wall, protrude 

 through an opening in the outer wall and grow out in the 

 form of a thread, which soon becomes divided into con- 

 secutive cells by transverse walls, gives off' side branches, 

 and develops root filaments or rhizoids. This cellular 

 thread is, as in the Liverworts, known as the protonema. 

 The cells which are exposed to light develop chlorophyll 

 granules, and the whole can thus live for a time as an 



* KsowLED&E, May, 189t?. 



independent plant. Repeated branching of the filaments 

 and the interlacing of their ramifications with those 

 developed from other spores frequently results in the 

 formation of bright green patches of felted threads, such as 

 may be commonly seen on moist clay banks. Apart from 

 characteristic colour, texture, and appearance under the 

 microscope, which soon become familiar by observation, 

 the most distinctive feature of the moss protonema is the 

 appearance on it of minute buds, which, as they increase 

 in size, are seen to be young moss plants. 



At various points on the protonemal thread little side 

 outgrowths appear, which become divided into upper and 

 lower cells by oblique partitions. From the lower cells 

 new threads grow out like those of the protonema, but 

 they remain colourless, penetrate the soil, and develop 

 into " root " filaments or rhizoids. The upper cells, by 

 continued elongation and repeated subdivision by longi- 

 tudinal and transverse walls, grow up into atrial shoots, 

 giving off leaves in succession behind the growing apex and 

 constituting the moss plant. The protonema, by spreading 

 over a relatively wide area, living and assimilating food, 

 and then producing numerous buds at different points, is 

 evidently of great importance in increasing the chances of 

 survival. 



It is with the reproductive processes of the plant that 

 we are at present concerned. Almost everyone knows by 

 sight the graceful capsules carried on slender stalks which 

 rise from the moss tufts of walls and woodland banks, 

 tree-trunks, and mountain rocks ; and almost everyone ia 

 content to regard them as a " moss fruit," growing at the 

 top of a continuation of the stem. It is only by a careful — 

 though by no means difficult — study of the tips of the moss 

 stems that we can find out the real meaning and mode of 

 origin of the " moss fruit." 



In the genus we have selected, fruiting is common 

 and conspicuous in most of the species. The antlieriilia 

 and aichi-gnnui occur on separate plants in the axils of 

 leaves at or near the apex of the stem. In the male plants 

 the tip of the stem is flattened out into a sort of " head " 

 or " capitulum," reminding one of the inflorescence of a 

 daisy or dandelion ; and on this will be found numerous 

 antheridia closely crowded together, but surrounded by 

 barren " hairs" or paniplii/ses — structures not met with in 

 the Liverworts. Looked at from above these give the 

 appearance of a round brown or black spot as large as a 

 pin's head, surrounded by a ring of spreading green leaves 

 considerably larger than those of the stem and often 

 differing in detail from them. In the female plants there 

 is no such marked modification of the tip of the stem, 

 though it is slightly enlarged in some species, and the 

 leaves round the archegonia may be slightly larger than 

 the ordinary leaves. It is best to select a tuft in the 

 early fruiting stage and examine those on which young 

 sporophytes occur, or the apparently sterile plants occur- 

 ring among these. 



To study these organs more carefully it will be best first 

 to cut longitudinally through the middle of a male flower 

 with a sharp knife, and examine with a lens. Among the 

 bases of the terminal leaves the antheridia will be seen as 

 elongated, straight, or slightly curved sacs. Mixed with 

 them are the numerous club-shaped hairs known as para- 

 phi/si-s, which do not occur in the Hepatics, and the use 

 of which is doubtful. By cutting a thin section with a 

 razor from the surface already exposed, and examining it 

 under a microscope, further details may be observed. The 

 antheridia will be seen to possess a thin wall composed of 

 one layer of cells ; and their granular contents appear 

 divided, by vertical and transverse walls, into a vast 

 number of minute cells. If one of them is in a ripe 



