LYCOPODINEAE. LIGULATAE. 287 



transverse divisions into cells that lie one above the other ; thus the neck is formed, 

 consisting in Selaginella of four rows of cells with two cells in each row, in Isoetes of 

 as many rows of four cells each. The lower of the first two cells, the inner cell, 

 thrusts a narrow prolongation in between the neck-cells, and this becomes separated 

 off as the canal-cell of the neck (Fig. 229 //); the lower and larger portion, the 

 central-cell of Janczewski, parts, as that observer states, with another small portion of 

 its protoplasm which answers to the ventral canal-cell of other Archegoniatae, and then 

 becomes the oosphere; the two canal-cells are converted into mucilage and ejected 

 through the opened neck in order to admit the spermatozoids to the oosphere. 



The spore-producing generation (sporophare, sporophyte}. Formation of the 

 embryo. In Isoetes as in the Filicineae the embryo is divided into octants by three 

 walls at right angles to one another ; the orientation also of the cotyledon, root and 

 foot is the same as in them, except that while the cotyledon as usual proceeds from 

 two octants, according to Kienitz-Gerloff the root requires not one octant, as is 

 usually the case, but two for its formation, and the foot four. There is nothing left 

 therefore for the apex of the stem, which does not seem very likely; I am inclined to 

 think that the stem proceeds from the same octant in Isoetes as in the Filicineae, but 

 that it is easily overlooked, because like the other organs in Isoeles it has no apical 

 cell and developes a leaf at a very early period ; the point requires further exami- 

 nation. Selaginella, in which Pfeffer has investigated the development of the embryo, 

 also varies in some points from the Ferns and Equisetaceae. The basal wall is at 

 right angles to the axis of the archegonium. The upper or hypobasal half of the 

 oospore by considerable elongation produces the suspensor, a structure which does not 

 appear in any other Vascular Cryptogam 1 but which occurs in almost all Spermaphytes 

 (Phanerogams) and thus brings Selaginella more closely to them. The suspensor 

 seldom remains a single cell ; one or more divisions usually appear in its lower part 

 (Fig. 232 A, B . . .). The embryo itself arises from the lower or epibasal half of 

 the oospore. By the elongation of the suspensor with compression and absorption 

 of the adjacent cells the mother-cell of the embryo is thrust downwards first into 

 the primary and then into the secondary prothallium, where the embryo is further 

 developed, as in the Gymnosperms. The transversal wall (Fig. 232 //) is now 

 formed in the mother-cell of the embryo at right angles to the basal wall (Fig. 232 /). 

 According to Pfeffer's account no median wall is formed. 2 , the succeeding walls being 

 all at right angles to the transversal wall (Fig. 232 II). On one side of these walls the 

 mother-cell of the stem (Fig. 232 s) is cut out by the wall ///, while the lower part of 

 the same half gives one cotyledon (Fig. 232 6), the other cotyledon proceeding from 

 the other half, which also gives rise to the foot. The rudimentary stem has a two- 

 sided apical cell, which gives off segments alternately right and left. An inner portion 

 of tissue soon becomes marked off as the initial strand of the axile bundle, and a 

 portion at the periphery as dermatogen and periblem. The expansion of the foot 

 forces the stem-segment over to the other side, so that the apex comes to be horizontal 

 and subsequently even to be turned upwards (Fig. 231 /) ; and finally when the 



1 [See Vines in Q. J. M. Sc. 1878.] 



2 It is quite possible however that a median wall is formed, for the question was approached 

 from a different point of view at the time of Pfeffer's researches; at all events a fresh investigation 

 would be desirable. 



