REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



241 



which the rudiment is composed. According 

 to Mr. Henfrey*, on the other hand, the germ- 

 cell is contained in the superior, and conse- 

 quently deeper, of the two portions into which 

 the primary nucleated parent cell of the organ 

 divides by a horizontal septum ; and is dis- 

 tinguishable before the formation of the pa- 

 pilla-like structure has commenced. This 

 account of the matter is not only supported 

 by analogy, but, as it appears to us, in a very 

 marked manner by Hofmeister's own drawings. 

 83. The embryo. Immediately after the en- 

 trance of the spiral filaments into the cavity of 

 the archegonium, the cells which immediately 

 surround it multiply rapidly, in consequence 

 of which the cushion-like projection of the in- 

 ferior surface of the prothallium increases in 

 size. At the same time the germ-cell is trans- 

 formed into an irregularly egg-shaped body, 

 which consists of minute cellules, and may be 

 considered as the primary axis of the future 

 fern. It originates in the same manner as the 

 rudiment of the fruit of the Mosses and 

 Hepaticoe, and elongates by repeated divisions 

 of a terminal cell by septa, inclined alter- 

 nately in opposite directions. It consequently 

 presents but one growing point, which is di- 

 rected, not towards the orifice of the archego- 

 nium, but, on the contrary, towards the centre 

 of the cushion-like mass, by the cells of 

 which it is surrounded. Soon after, however, 

 there appears on the side of the egg-shaped 

 embryo, which is directed towards the notch 

 in the anterior margin of the prothallium, a 

 second growing projection of its surface. This 

 projection, at first conical, becomes, as it 

 enlarges, compressed from above downwards. 

 No sooner is this the case, than it bursts through 

 the superficial cellular layer of the prothallium, 

 at a point which is invariably a little anterior 

 to the base of the archegonium between it 

 and the angle of the notch. It now assumes 

 the form of a symmetrical leaf-like organ, and 

 begins to project beyond the notch of the 

 prothallium. The further development con- 

 sists in the appearance in the axil of this 

 primordial leaf, of a new axis, the permanent 

 stem of the young plant. From this axis all 

 the succeeding leaves take their origin, each 

 diverging from its immediate predecessor at 

 an angle of 60. 



84". Sporangia and spores. At a point of 

 the surface of the frond, which always cor- 

 responds to the termination of a vascular 

 bundle, a lacuna is formed under the epider- 

 mal layer, by the separation of that structure 

 from the subjacent tissue. The floor of this 

 cavity consists of a pavement of tessellar 

 cells, some of which grow out into nipple- 

 shaped projections. In each of these, the 

 projecting portion is separated from the rest 

 by a horizontal septum, which is soon fol- 

 lowed by several others superior and parallel 

 to it. The last-formed terminal cell now en- 

 larges, and assumes a globular form, and is 

 converted by a process similar to that to be 



* On the Development of Ferns from their Spores' 

 Trans. ofLinnajan Society, vol. xxi. p. 135. 

 Supp. 



described below in the rudimentary sporan- 

 gium of Equisetum, into a central mass of 

 nucleated cells, with grumous contents (parent 

 cells), enclosed in a capsule formed of a single 

 layer of others, which are tabular. In each 

 parent cell, the central nucleus afterwards 

 disappears, and is replaced by four others. 

 This is followed by the division of the pri- 

 mordial sac into four portions, around each 

 of which a cellulose membrane is formed. 

 This membrane becomes the epispore; asecond 

 (endospore), which is distinguished by its 

 greater delicacy, being subsequently formed 

 within it.* 



85. Equisefacece.The history of the deve- 

 lopment of the Equisetaceae corresponds in 

 most respects with that of the Ferns. 



86. First period.-^ Germination of the spore. 

 The spore of Equisetum consists, in its ripe 

 condition, of a delicate, colourless internal 

 vesicle, which is surrounded by a more or less 

 resistant granular membrane, and contains a 

 central nucleus, and a yellowish grumous fluid, 

 in which swim oil and chlorophylle granules. 

 The first change observed in germination con- 

 sists in the division of the nucleus into two, 

 and the subsequent formation of a septum 

 between the two corresponding halves of the 

 spore-cell. Of these halves, the larger con- 

 tains nearly all the chlorophylle, and is de- 

 veloped to the stem; thesmaller,thecontents of 

 which are almost colourless, is the commence- 

 ment of the root. The prothallium, which 

 results from repeated cell-division of the larger 

 half, is an irregularly riband-shaped expan- 

 sion, growing and branching repeatedly at the 

 extremity furthest from its point of origin, 

 and consisting of large, delicate-walled cells, 

 containing much chlorophylle. One of the 

 branches is usually observed to be larger than 

 the rest, and it is upon it that the reproductive 

 organs a> - e formed. 



87. Antheridium . The rudimentary antheri- 

 dium of Equisetum consists, like that of pre- 

 ceding families, of a papilla, composed of foul- 

 conjoined vertical piles of cells, each pair 

 slightly overlapping the pair preceding it. In 

 each of the cells constituting this rudiment a 

 tangential wall is formed, dividing it into an 

 inner three-sided, and an outer tabular cell. 

 The inner cells, which form a central oval 

 mass, are soon observed to be filled with finely 

 granular mucus : the tabular cells, on the con- 

 trary, contain chlorophylle, and form the wall 

 of the future antheridium. The further de- 

 velopment of the central mass corresponds 

 entirely with what has been described in other 

 families. The antherozoa are larger in Equi- 

 setum than in any other known example. 

 They originate by the deposition of a gela- 

 tinous linear thickening, in the form of an 

 imperfect ring, parallel to the plane surfaces of 

 the discoid vesicles in which they are enclosed. 

 When fully formed, they resemble, in almost 



* Schacht, Entwick. des Sporangiums einiger 

 Farrnkraeuter Bot. Zeitung, 1819. p. 537. 



f Hofmeister, /. c. pp. 97103. ; Milde, Entwicko- 

 lungsgeschichte der Equiseten, &c. Bonn, 1852. 



it 



