DEVELOPMENT OF THE OSTRICH FERN. 47 



strong'ly revohite (PI. 7, fig". 10), that the whole lower surface of the lobes is com- 

 pletely covered, the margins acting as an indiisimn. 



The young sorus (fig. 11) arises as a small prominence above a young vein, and is 

 formed by a rapid groAvth of cells at and just below the sui'face. This prominence soon 

 becomes hemispherical, and the formation of the sporangia begins. These arise as 

 j^a^jillae from the superficial cells of the receptacle and ai-e, therefore, morphologically, 

 trichomes. 



All the cells of the young receptacle are colorless, filled Adth fine granular protoplasm, 

 and distinctly nucleated. The cell from which the sporangium is to arise (fig. 13, m) 

 soon becomes slightly convex, dividing then by a wall parallel to the siu'face into two 

 cells, an outer and an inner, the former (fig. 11) being the mother-cell of sj)orangium, 

 the other taking no further part in the formation of the sporangium. Sometimes, but 

 not usually, the oi'iginal cell appears to undergo a preliminary division before the mother- 

 cell of the sporangium is cut off. The mother-cell rapidly enlarges, assuming first a 

 hemispherical form, and then elongating so as to become rather pear-shaped. After 

 reaching this stage it is divided by a wall parallel to that by which the mother-cell was 

 foraied, into two cells, the lower of which forms the pedicel, the upper the cajjsule of the 

 sporangium (fig. 15). In the earlier sporangia the upper cell undei'goes several divi- 

 sions before any more are formed in the lowei- one, but in those formed later, the pedicel 

 lengthens rajiidly in order to bring the young sporangium on a level with those previously 

 formed, and it undergoes several di^asions very early, so that on examining an older so- 

 i"us, it is not at all uncommon to find very young sporangia in which the pedicel is many 

 times longer than Avould be the case in those of the same age taken from one of the 

 younger sori. 



The fii'st diAasion in the capsule is nearly vertical, but usually slightly inclined, so that 

 the resulting cells are not quite of equal size (fig. IG). FolloAving this is a second 

 Avail inclined to the first at an angle of about 60", and next a third, parallel to the outer 

 Avail of the capsule, and meeting both of those already formed (figs. 16-19). If a sporan- 

 gium is now examined from aboA^e (fig. 19) , it will be seen that both edges of the first Avail 

 are in contact Avith the outer Avail of the capsule; that the second has one edge in contact 

 Avitli the first Avail, and one Avith the outer Avail of the capsule; while the third, Avhich is 

 nearly triangular in form, touches the Avail of the capsule Avith its ujiper edg'e only, the 

 other tAVO being in contact respectively Avith the first and second. Finally a fourth wall is 

 formed parallel to the uppei- surface of the cajjsule, but not touching its outer Avail at any 

 point, its three edges being in contact Avith the three walls just described (figs. 18-20). 

 The capsule noAV consists of fiA'e cells, four parietal ones, tabular in form, and a central 

 tetrahedral one, the arcJ/esjMrinm. By the time that the capsule has reached this stage, 

 the jaedicel has usually imdergone division by a longitudinal wall, into two unequal cells 

 (fig. 20) . The larger of these divides again by a second longitudinal Avall, and the three 

 cells thus formed become divided by a series of transA^erse Avails, so that the pedicel when 

 comjilete consists of three roAvs of cells. These are short at first, except in the later formed 

 sporangia, but finally become about four times as long as broad (figs. 21, 26). 



The archespoi'ium now becomes divided by Avails parallel to the first Avails foi'uied in 

 it, and dcA^eloped in the same order (fig. 21). These are the primary tapetal cells, and, 

 Avhile they are forming', the })arietal cells undergo further divisions I)A' Avails ])eri)endicu- 



