60 FIRST GROVP.-^THALLOPHYTES. 



mucilage, and make" their way from thence into the oosphere, the wall of which has 

 become mucilaginous in its upper part. After fertilisation the oospore becomes 

 invested with a wall of cellulose and the chlorophyll-corpuscles of the envelope assume a 

 reddish-yellow colour ; the walls of the enveloping tubes adjacent to the oosphere 

 thicken and become lignified and of a black colour ; thus the oospore acquires a hard 

 black coat, and falls to the ground to germinate there in the ensuing autumn or in 

 the next spring. 



The history of the development of the antheridia and oogonia is as follows. 



The sequence in the. formation of the cells of the antheridium has been fully described 

 by A. Braun in Nitella syncarpa and Chara BaueH ; it agrees with that in Nitella 

 flexilis and Chara fragilis . In Nitella the terminal cell of a leaf becomes an antheri- 

 dium ; the oldest leaf in a whorl is the first to form its antheridium, the others follow 

 according to age; the antheridia may be seen immediately after the appearance of 

 the leaf- whorl. Fig. 38, A, gives a longitudinal section through the apex of a shoot, of 

 which / is the apical cell ; the last segment formed from it has already divided by 

 a transverse wall into a nodal mother-cell K and an internodal cell beneath it ; 

 beneath the internodal cell is the node of the stem with the last whorl of leaves ; b is 

 its youngest leaf, bK the basal node of the oldest leaf, which consists already of 

 the segments /, //, ///; a is the terminal cell of this leaf which is being transformed 

 into an antheridium. While the spherical antheridium is being formed, the leaf also suffers 

 changes which should first be considered. The segment ///becomes the first internode 

 of the leaf, // the first node, which developes the lateral leaflet nb in C and D. 

 The cell / divides into two (C, /), of which the lower remains short, while the upper 

 grows into the flask-shaped cell /in Fig. 38, Z>, and Fig. 39. 



The spherical mother-cell of the antheridium (Fig. 38, A, a) divides first by a wall, 

 which is radial and vertical in relation to the axis of the branch, into two hemispheres, 

 and these are converted into four quadrants by vertical walls at right angles to the first 

 wall ; a third division, horizontal and at right angles to both the former walls, takes 

 place in each of the quadrants and simultaneously in all four, and now the antheridium 

 consists of four upper and four lower octants of a sphere. Contraction by means of 

 glycerine shows distinctly that in each of these processes of division the protoplasm is 

 completely divided before the appearance of the wall of cellulose (Fig. 38, /?) ; the 

 second division takes place even before the wall is developed between the two halves 

 which were first formed ; it is possible to make the four quadrants contract before the 

 wall between them is visible ; in Fig. 38, B, the third division has just taken place, the 

 second vertical wall is already formed, the two quadrants there visible are already 

 divided, but no horizontal wall is yet formed. Fig. 38, A, a, shows the eight octants with 

 their nuclei in perspective. Each octant now first divides into an outer and an inner 

 cell (Fig 38, C] ; the latter is again divided in all the eight octants, so that now. each 

 octant consists of an outer, a middle, and an inner cell (D, e, m, z). Up to this time the 

 sphere continues solid, all the cells are in close contact with one another ; but now 

 begins unequal growth and with it the formation of intercellular spaces (Fig. 39). The 

 eight outer cells (e) are the young shields, the lateral walls of which showed at an earlier 

 stage the radial infolding already mentioned ; they grow more strongly than the inner 

 cells in a tangential direction, the outside of the sphere enlarging more rapidly than the 

 inside ; the middle cells (m), the manubria, continue attached to the shields, but are 

 separated from one another by the tangential growth of the sides of the shields ; they 

 grow slowly in the radial direction ; the innermost cell (*) of each octant is rounded oft 

 into a head-cell. The cell (/) in Fig. 38, D, increases rapidly in size, thrusts itself 

 between the four shields into the interior of the sphere, and becomes a flask-shaped 

 cell, on whose apex the eight head-cells rest. Fig. 39 shows this condition of the 

 antheridium in optical longitudinal section ; where the walls of the head-cells border on 

 the intercellular spaces which are now formed and are filled with fluid, they put out 

 branches (r) which become divided into cells by transverse septa and branch again ; these 



