APPENDIX. 



463 



a layer of hard tissue (sclerenchyma), consisting of fibres. 

 If the older part of the stem is cut off and steeped in water 

 or dilute hydrochloric acid for some days, the soft ground 

 tissue can easily be removed by using a hard brush, the 

 bundles remaining behind as a skeleton. This skeleton 

 resembles a piece of wire netting rolled up into a tube ; the 

 meshes of the network correspond to the insertions of the 



VEIN 



SPORANGIA 



Fig. 4. Sporangia of Male Pern. 

 Transverse section through a pinnule and sorus. 



leaves, and are called the foliar gaps, while the bundles 

 passing out to the leaves are given oft* as branches from the 

 edges of these gaps (Fig. 2). 



On examining a leaf in summer, one sees a number of 

 small kidney-shaped projections on its lower surface, arranged 

 in two rows on each of the divisions of the leaflets. These 

 projections are at first of a light green colour, but when older 

 they become brown. These are the sori (Fig. 3). Each sorus 

 consists of a collection of small stalked bodies, the sporangia 

 or spore-cases, and on removing the kidney-shaped structure 

 (which covers the group of spore-cases and is called the 

 indusium), it is fairly easy to make out that the spore-cases 

 are all attached to a little projection of the leaflet, called 

 the placenta, and that this placenta is seated on one of 

 the veins (Fig. 4). The veins of a fern leaf end in a very 



