I] 



VEGETATIVE PROPAGATION 



the rhizome forks frequently. Whenever progressive rotting extends from 

 the base beyond a branching, the two apices grow on as independent plants. 

 In this way the Bracken multiplies habitually. 

 In Dryopteris buds are formed near the bases 

 of the leaves in old plants. Again, as rotting 

 proceeds from the base, these buds become iso- 

 lated, and root themselves as new individuals 

 (Fig. I, B, C). In other Ferns, as in the various 

 species of Asplenium so commonly grown in 

 dwelling rooms, buds or bulbils arise on the 

 lamina. Being very lightly attached to the leaf 

 they are readily shed, and root themselves inde- 

 pendently in the soil. In some cases vegetative 

 buds may replace the sori (Fig. 13). Such vege- 

 tative propagation of the Fern-Plant is a mere 

 repetition of the sporophyte generation. But 

 sooner or later the Fern-Plant bears the spores, 

 which start the alternate generation. 



The spores are produced on certain leaves 

 of the mature plant which are therefore called 

 sporophylls, to distinguish them from those which 

 are only nutritive. In Dryopteris nutritive 

 leaves and sporophylls are alike in outline 

 (Fig. 2). The young plant only produces the 

 former. But the leaves of older plants bear on 

 their lower surface, and chiefly in the apical 

 region, numerous groups of organs which are 

 green or brown according to age. These are 

 called so7-i, and consist of sporangia with certain 

 protective structures. The sori vary greatly in 

 size and form in different Ferns, which are classified according to their 

 characters. In Dryopteris, as its old name NepJirodiimi implies, they are 

 kidney-shaped, as is seen in Fig. 2. Each sorus is seated on a vein, which 

 provides its necessary nourishment. It is protected by a covering called the 

 indusium, of kidney-like outline, beneath which are numerous sporangia. 

 If a leaf bearing mature sori be laid on a sheet of paper to dry, with its 

 lower surface downwards, the indusia shrivel, and the bursting sporangia shed 

 the spores in such numbers that they give a clear print of the outline of the 

 sporophyll upon the paper. The spores are dark-coloured, very minute, and 

 are produced in millions. 



A vertical section through the sorus of Dryopteris shows an enlarged 

 receptacle, traversed by the vascular strand. The indusium rising from it 



Fig. 1 3. A pinna of a Fern ( Wood- 

 wardia) showing many sporo- 

 phytic buds on the upper surface. 

 They correspond in position to 

 sori on the lower surface, which 

 are abortive, and so they may be 

 held to be substitutionary growths. 



