Ferns 



213 



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being quite round and attached to the centre of the heap by an almost 

 imperceptible stalk, while in Nephrodium, although similarly attached, the 

 cover is definitely kidney-shaped, the attachment being at the deep in- 

 dentation. Blechnum and Lomaria, two very similar genera, bearing the 

 spores on upright contracted fronds springing from a rosette of leafy ones, 

 are often confused even by the botanists who have determined the differ- 

 ence, which is that in Lomaria the lines of spore heaps are purely marginal, 

 with the margin turned backward to act as indusium, while in Blechnum 

 the heaps or lines are only near the margin, which is unaltered, a distinct 

 and independent indusium arising between it and the 

 spore heaps. From what we have stated, it is clear that 

 a little study devoted to the forms in which the spores 

 are borne is of great assistance in determining to what 

 species the plant concerned belongs, apart from the 

 general appearance, which may mislead. 



Having thus dealt with the spore, or rather the spore 

 heap, as a discriminating feature for 

 Fern identification, we may now go 

 a step further and consider how this 

 unfertilized one-celled simple body 

 can effect its task of engendering a 

 new generation, involving as this 

 does something equivalent to flowers 

 and the two sexual interacting ele- 

 ments which flowers produce prior to 

 the evolution of a fertilized seed 

 capable of yielding a young plant. 

 A seed, as we know, enjoys the ad- 

 vantage of containing not merely 

 a fertilized germ but ajso a store 

 of nourishment with which the 

 mother plant had endowed it after the fertilization was effected in order 

 to give it a start in life. The spore possesses no such advantage; it is 

 only endowed with sufficient vitality to swell under congenial conditions 

 of warmth and moisture, and, bursting the husk, to protrude a self- 

 engendered root-like cell which attaches itself to the soil; and by virtue 

 of the nourishment obtained therefrom and from the air through the 

 chlorophyll, which even at this early stage it contains, it slowly forms, 

 first a short chain of cells (fig. 306) and then by lateral multiplication as 

 well, it builds up a heart-shaped dark-green growth (fig. 307) about the 

 size of a herring scale, which is firmly rooted to the soil by innumerable 

 root hairs or rhizoids, mainly springing from the first-formed part of the 

 " prothallus ", as this body is termed. Viewed from above, the prothallus 

 looks simple enough, and resembles anything but a Fern, a fact which 

 rendered the origin of young Ferns a profound mystery until so recent a 

 date as 1846, when Count Suminski discovered the final stage in the normal 



Fig. 306. A Young Pro- 

 thallus arising from a Spore 



Fig. 307. Young Fern 

 Plant 



p.Prothalliuni; r^rhizoid; 

 r, root 



