SPECIAL MORPHOLOGY: RHIZOCARPE^E. 207 



ledon, since the proper terminal bud does not become developed on 

 account of its intimate connection with that cellular layer investing the 

 embryo-sac, already alluded to. The difficulty of drawing this parallel 

 in the discoid cotyledon of Salvinia is only apparent, if we take the 

 cotyledon of Lemna, for instance, as the basis of the comparison. The 

 first lateral bud growing forth then forms a horizontally advancing stem, 

 a rhizome (rhizoma), wholly agreeing with so many Phanerogamia, as, 

 for example, Asparagus. In Salvinia no further development of the 

 radical extremity occurs, but in Pilularia a root (fig. 150. e), which is 

 to be regarded as an adventitious root, is always produced on the side of 

 the stem, exactly opposite the bud, immediately beside the firmly at- 

 tached radical point. 



117. On the full-grown plant are formed, from the lower part 

 of the leaf-stalk (in Marsilea quadrifolia), or at its base (Marsilea 

 pubescens, Pilularia), little nodules, which subsequently grow out 

 into a fruit, borne upon a stalk, which is sometimes long, some- 

 times short, or (as in Salvinia) a little branch springs from the 

 base of the leaf-stalk, hangs down in the water, and produces a 

 number of little fruits arranged upon it in the form of a spike. 



The fruit of Marsilea is nearly ovate, compressed on two sides. 

 A tough, coriaceous coat, subsequently opening in two valves, 

 surrounds a cavity which is divided into two chambers by a lon- 

 gitudinal septum, imperfect at the upper part, and each of these 

 compartments is again divided by transverse septa into from five 

 to twelve chambers. From the region of the point of attachment 

 of the fruit, on the upper side, where the longitudinal septum is 

 wanting, runs a cord of gelatinous cellular tissue, wholly free 

 except at that point of attachment, which bears on each side from 

 five to twelve little sacs, also composed of gelatinous cellular 

 tissue, and hanging down in these lateral chambers. Through 

 these sacs, almost entirely on the outer side, runs a cord of dense, 

 but also gelatinous, cellular tissue ; and the two kinds of repro- 

 ductive organs are attached to this in such a manner that the seed- 

 sacs, fewer in number, only occupy the more central portion, that 

 next the longitudinal septum. The stalked seed-sacs so enclose 

 the already described seed-buds that the nucleus is turned toward 

 the stalk ; they subsequently dehisce. The anthers are irregular, 

 pyriform sacs, containing a great number of pollen-granules, which 

 are composed of a pollen -cell, external pollen-membrane, and in 

 addition to these a special gelatinous coat. 



The fruit of Pilularia is globular. The equally tough, coria- 

 ceous coat, subsequently dehiscing in four valves, surrounds a 

 cavity which is divided into four chambers by vertical septa. In 

 the middle of the outer wall of each chamber runs a cord of gela- 

 tinous cellular tissue, which bears the anthers and seed-sacs on its 

 inner side. The latter are distinguished from those of Marsilea by 

 the nucleus lying on the side opposite to the stalk. Here, also, the 

 seed sac dehisces, and allows the seed-bud to escape. The anthers 

 are like those of Marsilea, but the pollen-grains want the gela- 



