62 FIRST GROUP. THALLOPHYTES. 



(A, b] bears the'smaller nodal cell with the five rudimentary enveloping tubes (A), only two 

 of which are here seen in longitudinal section ; above the nodal cell is the apical cell (s) 

 of the shoot. (B} shows a further stage of development ; the first of the cells called by 

 Braun the * Wendungszellen ' (or) has made its appearance, and two transverse septa 

 have been formed in the upper portion of each of the enveloping tubes ; these short 

 upper cells are raised by the intercalary growth of the tubes above the apical cell and 

 form the crown K in C and D. The lower of these two cells puts out a process which 

 projects inwards and downwards, as C and D show, so that the five lower crown 

 cells together form a sort of weel (eel-basket) opening downwards. After a time 

 the enveloping tubes begin to assume the spiral torsion, the coils constantly taking 

 a more horizontal direction, while the apical cell of the shoot enlarges considerably and 

 becomes the oosphere (Fig. 37). The development and fertilisation of the oogonium in 

 the genus Chara has recently been described at length by De Bary in Chara foetida. 

 Here too, as in Nitella, it consists at an early stage in its existence of an axile row of 

 three cells, and of five rows of two cells each forming an envelope round the former. 

 The lowest cell of the axile row is the nodal cell : the second is here also always small 

 and colourless and answers to the ' Wendungszellen ' of Nitella, and, as De Bary's 

 figures show, is cut off by an oblique septum from the base of the apical cell, which is 

 now the third of the axile row. The apical cell, at first almost hemispherical, becomes 

 ovoid-cylindrical and ultimately ovoid in shape ; until it reaches its full size its cell-wall is 

 very thin and delicate ; its protoplasm is rich in drops of oil and starch-grains except 

 at the apex, where there is a transparent terminal papilla, the receptive spot, with finely 

 granular protoplasm ; in this state the apical cell of the oogonium is the oosphere. The 

 five enveloping tubes are from the first closely applied to the apical cell ; after each has 

 been divided in two by a transverse wall about half-way up, the upper cells thus divided 

 off unite closely with one another above the apical cell ; the envelope is thus closed all 

 round, at least in the case of Chara foetida, before the ' Wendungszelle ' separates from 

 the oosphere. The five upper cells of the envelope are at first of the same length as the 

 five lower ; the dividing septa are about half-way up the oosphere ; but as the oosphere 

 grows, the five lower cells grow into long tubes, which are at first straight and after- 

 wards become twisted spirally round the oosphere. The five upper cells form the 

 crown, which is raised some distance above the apex of the oosphere. Between the 

 crown and the apex of the oosphere the tubes of the envelope grow inwards and increase 

 in breadth, and form above the apical papilla of the oosphere a thick diaphragm open 

 only in the middle, and separating a narrow space beneath the crown from a still nar- 

 rower space above the oosphere. The cells of the crown form a lid over the upper space ; 

 the upper and lower space communicate by the narrow opening in the diaphragm. De 

 Bary finds a similar construction in Nitella. As soon as the oogonium has reached its full 

 size, the small space above the diaphragm becomes enlarged by the elongation of the 

 tubes between the diaphragm and the crown ; this portion of the envelope, thus late in 

 enlarging, De Bary calls the neck ; at this part the five tubes separate from one another 

 and form five fissures beneath the crown and above the diaphragm. 'Through the fissures 

 the spermatozoids force an entrance in numbers into the apical space, which is filled 

 with a hyaline mucilage ; that one or more find their way to the oosphere is rendered 

 less doubtful by the circumstance, that the papilla at its apex is invested at this period 

 with a very thin cell-wall or with none, as is shown by the extrusion of its contents into 

 the apical space on very slight pressure. 



Braun's account of the morphological value of the oogonium of Chara is fully 

 confirmed by Fig. 41, A, which represents the lower portion of a young full-grown 

 leaf of Chara fragilis with the adjoining piece of the stem and an axillary bud in 

 longitudinal section : m is half of the nodal cell of the stem, / its upper, t its lower 

 internode ; sr a descending, y an ascending cortical lobe ; sr the cortical lobe of the 

 lower internode which descends from the leaf, rk one of its nodes ; i" is the first inter- 

 node of the axillary bud resting on the cell , which connects the stem-node m with the 



