FI LTC ALES LEPTOSPORANGIATAE 269 



period of rest as there is in flowering-plants when the seed is ripe. 

 The prothallus continues to assimilate food and supply the young fern 

 until the latter is able to do so for itself. The primary root remains 

 small or withers away, and new ones are adv. formed from the stem 

 or from the 1. bases, as the pi. grows. The mature pi. may be of 

 almost any size from the tiny filmy ferns (Hymenophyllum) to the 

 large tree ferns (e.g. Cvathea, Alsophila). The stem grows by an 

 apical cell, 2- or 3-sided, cutting off segments alt. on each face. 

 From these by further divisions arise the tissues and members. The 

 1. form a little way behind the growing apex as in fl. pi. One segment 

 (but not every one) gives one 1. ; the 1. grows by an apical cell also. 

 The stem may be erect, or may climb (as in many epiph.), or creep 

 on the surface, or below it as a rhiz. Its growth is slow and branch- 

 ing infrequent. The 1. are borne upon it, the internodes being as a 

 rule short in erect, long in creeping stems. The phyllotaxy is not so 

 definite as in fl. pi., but the 1. are very commonly in ranks or straight 

 lines dependent on the position of the segments cut off from the 

 apical cell of the stem. The lat. buds arise either on the 1. (as in 

 Dryopteris, Nephrodium) or on the stem ; in the latter case they 

 are rarely axillary; but usu. beside the 1. The growing tips of stem 

 and 1. are often protected by brown scales, which are mere trichomes 

 or superficial outgrowths. 



The I. is usu. large with apical growth and circinate (coiled) 

 vernation. The growth often lasts for a long time, or even perma- 

 nently (Lygodium). The 1. blade is usu. branched pinnately. 



The repr. organs are borne upon the 1. The unit is the sporangium 

 or spore capsule, a small rounded body, stalked in fams. 2, 3 and 8 

 but sessile in the others. The caps, has a wall one cell thick, and in 

 this is a group of cells with peculiarly thickened cell-walls, termed 

 the annuhis, by whose agency (its cells being hygroscopic) the opening 

 of the sporangium is effected. Sometimes, as in many Polypodiaceae, 

 the opening is explosive. The mech. is in principle similar to that 

 by which anthers dehisce. The annulus may have various forms (see 

 fams.), but the commonest is that of a row of cells running round the 

 sporangium for about f of its circumference. 



The sporangia are usu. collected into groups (sort). The sorus 

 may be naked, but is more usu. covered by an indusium, some- 

 times merely a fold of the 1. itself, but more commonly a special 

 outgrowth from the ]., either epidermal or derived from the more 

 deeply placed layers of tissue as well. The sori are usu. found on 

 the veins of a 1., often in the angle where a vein forks. They do not 

 as a rule occur on all the 1. Very often certain 1. are fertile, the 

 others not. In this case the fertile 1. have usu. no green tissue at 

 all, their pinnae being entirely covered with sori, e.g. Osmunda sp. 

 In other cases, e.g. Aneimia sp., one part of a 1. is sterile, the other 

 fertile. Or again the sori, and this is most common, may be borne 

 simply on the ordinary 1. They are almost always on the lower 

 surface only; they may entirely cover it, but more often are localised. 



The spores are all of one kind and if sown under suitable condi- 

 tions give rise to prolhalli, flat green expansions living for a short or 

 long period independently upon the soil (numbers may be seen where 



