HARDWICKE'S SCIENCE-GOSSIP. 



241 



GRAPHIC MICROSCOPY. 



By E. T. D. 



No. XI. — SoRi OF Fern : Makattia alata. 



HE outward appear- 

 ance of the fruc- 

 tification of ferns 

 has always attract- 

 ed observation, 

 groups and species 

 affording great 

 variety of forms 

 variously situated, 

 united with per- 

 fect symmetry, and 

 in many cases 

 exhibiting beauty 

 and interest of an 

 ex t r aor dinary 

 character. 



The under-side 

 of a frond, as well 

 known, reveals 

 yellow, dust -like 

 spots, lines, or patches, made up of groups, or 

 masses of receptacles (the sori) containing, or com- 

 posed of, a number of minute cases (the sporangia). 

 Their positions greatly differ, and they are scat- 

 tered over the under-side of the frond, localised in 

 various parts, or confined to the very edge ; they 

 originate and are developed in the tissues, in contact 

 with a vein, beneath the cuticle of the leaf, a 

 portion of which is forced up as the receptacle 

 is developed and presses for room, and often 

 remains as a delicate membrane which eventually 

 constitutes a protecting cover, (the indusium). As 

 maturity increases, the indusium becomes partly 

 detached, sometimes entirely, and eventually it either 

 shrivels up, or falls off. In some ferns it opens in the 

 centre and surrounds the sori, like a frill, forming a 

 cup ; in other species, the epidermis of the leaf is 

 raised into ridges, including and protecting the sori 

 beneath, thus fulfilling the functions of an indusium. 

 The form and position of these receptacles and the 

 presence or absence of the indusium are peculiarities 

 bearing upon the distinction of genera. 

 No. 239. — November 1884. 



The spore cases may be popularly described as 

 globular boxes, which, in some cases, are encom- 

 passed by an elastic ring (the annulus). The tension 

 of this band, breaks open and fractures the little case, 

 releasing and scattering its contents. The presence 

 or absence of this annulus, has led to the division of 

 ferns into two groups — the Annulate, and the Exan- 

 mtlate. The Marattiace?e are included in the latter, 

 being destitute of this peculiarity ; the dispersion of 

 the spores is effected by the separation of the two 

 halves of a compound and united sporange, which 

 splits longitudinally, not unlike the pod of a pea, as 

 seen in the plate. 



Marattia alata is a native of the West Indies, but 

 specimens of the fronds in fructification may l)e easily 

 procured, as the plants are found in almost every 

 collection of tropical ferns. 



Beautiful as the general elegance of the little 

 clusters of sporangia on any fern may be, when seen 

 with a low-power and good reflected light, deeper 

 interest is excited in tracing the future of an in- 

 dividual spore in countless thousands packed 

 in their little cases. 



These mere specks or particles, which in their 

 minuteness might be scattered into comparative in- 

 visibility, exhibit a most marvellous process, only 

 revealed by the aid of fine and high magnifying 

 powers. 



In flowering plants, fertilisation and the mature 

 seed is a final result ; in the ferns this process is 

 reversed, fertilisation curiously fjllowing the com- 

 mencement of a cell development, but preceding 

 the establishment of the ultimate growth ; and this 

 wonderful power is potential in each individual 

 spore, always microscopic, however large or grand in 

 dimensions the perfected plant may be, and many 

 tropical ferns assume tree-like dimensions. 



To reach this exhibition of innate power, a well- 

 ripened frond of an English hardy species should be 

 dusted on the surface of a porous brick, placed in a 

 shallow pan of water, the whole covered with a bell- 

 glass, and, placed in a ^\arm and shady corner, the 



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