25* REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



to the axis of the frond. This is followed on 

 each side by transverse, and afterwards by 



Fig. 200. 



r 



Vertical section of floor of gem-pouch of Lunularia, 

 50 diam. 



The club-shaped rudiments of the gems are attached 

 by their bases to the superficial layer of cells, 

 which are much smaller than those upon which 

 they are supported. 



vertical septa, which last are parallel to it. 

 Hence results a bilateral organ, the surfaces of 



Fig. 201. 



Mode of origin of the gem. 



Two of the cells of the superficial layer are seen 

 more highly magnified. The membrane of each 

 has grown out into a nipple; in one the vertical 

 septum can be distinguished. 400 diam. 



which are at right angles to the axis of the 

 frond. Its form is at first that of a flattened 



Fig. 202. 



a flattened rudiment of the gem viewed laterally. 

 Division of the second cell of the rudiment by a 

 vertical septum, on each side of which the com- 

 mencements of several transverse septa are mo- 

 delled out in the protoplasma. 400 diam. 



b, the same at a later stage, 250 diam. 



club : afterwards, as it becomes larger, two 

 notches are formed on each of its lateral 

 margins, which exactly resemble those of the 

 anterior margin of the young frond. As soon 

 as its development is completed that is, when 

 it has attained a length of about 1 of a line, 

 it is pushed out of the receptacle by its rapidly 

 growing successors. If, after its expulsion, it 

 is sown on a damp surface, a new growth at 

 once commences in two opposite directions, 

 in a line which is at right angles to its axis. 

 At the same time the cells of the inferior sur- 



face grow out into nipple-shaped projections, 

 which soon become filamentous roots, and the 

 whole is transformed in toa riband-shaped frond. 



The organ, the development of which is de- 



Fig. 203. 



' Outline of gem as observed two or three days after it 

 has been sown, 50 diam. 



In its inferior margin is a notch which indicates its 

 point of attachment to the floor of the gem- 

 pouch. The other two notches, one on each side, 

 are the points of growth of the young plant into 

 which the gem is transformed : they resemble 

 those which are described ( 58.) in the margins 

 of the young frond of Anthoceros. It is remark- 

 able that the line of direction of growth of the 

 young plant is at right angles both to that of 

 the gem itself, and to that of the parent plant. 



scribed above, receives, in common with others 

 of a different nature, the name of "gem." 

 The whole process differs widely from that of 

 true gemmation or " rejuvenescence " of an 

 old cell, iu order that its primordial vesicle 

 may be transformed into an embryo. This 

 distinction is well illustrated in the gemmation 

 of Anthoceros ; the primordial sac of a cell of 

 the parenchyma of the frond, the position of 

 which is undetermined, contracts and secretes 

 on its surface a new cellulose membrane. 

 The new cell is converted by repeated division 

 into the rudiment of a young frond, which, as 

 it grows, breaks through the tissue of the 

 parent. In Jungermannia bivaricata, we have 

 observed a similar process. A single cell of the 

 leaf of a marcescent, last year's stem, is seen 

 still to contain a primordial vesicle, lined with 

 green protoplasm. This forms around itself a 

 new cell, which divides by a septum, the direc- 

 tion of which is transverse in relation to that of 

 the first growth. One of the resulting cells grows 

 out so as to project through, or carry before 

 it, the membrane of the old cell. This divides 

 by a septum inclined obliquely to the former, 

 which is succeeded by another, inclined in the 

 opposite direction, and so on alternately. 

 Hence results the rudimentary stem of a new 

 plant. Both of the preceding are examples of 

 gemmation. 



The very distinct analogies in development 

 (homologies) which present themselves among 

 the higher plants, are exhibited in the following 

 table. The six last vertical columns represent 

 the principal groups, which follow each other 

 in the same order as in the preceding pages. 

 In the two first columns are indicated those 

 more partial analogies which may be traced 

 between the higher plants, on the one hand, 

 and the Alga;, Fungi, and Lichens on the 

 other. 



