FORMATION OF CELLS. 



page 4) ; the whole contents of a vegetative cell of a filament contracts, expels a 

 portion of the water of the cell-sap ; the arrangement of the differentiated proto- 

 plasmic body is changed, the bands of chlorophyll disappear ; its form alters as it 

 escapes from its cell-wall ; from almost cylindrical, 

 the protoplasmic body becomes ovoid, and shows a 

 broad green and a narrower hyaline end ; after the 

 swarming is completed, the latter becomes the base, 

 the green end alone grows at the apex as soon as the 

 new cell clothes itself with a cell-wall. The observa- 

 tions of Pringsheim on Oedogonium also show that 

 the direction of growth of the renewed cell is at right 

 angles to the original direction of growth before the 

 renewal ; for the hyaline, or rooting-end of the swarm- 

 spore, which afterwards attaches itself, is formed on 

 the side (Fig. 4, ^, E), not at the upper or lower 

 end of the protoplasmic body. An essentially differ- 

 ent arrangement in space of the entire protoplasmic 

 body of the cell also takes place ; the transverse be- 

 comes the longer diameter of the cell and of the plant 

 arising from it. The material remains, as far as can 

 be seen, the same, but its arrangement is different ; 

 this is morphologically determinate, and every new 

 formation of cells depends essentially on a fresh 

 arrangement of protoplasm already in existence ; 

 hence the rejuvenescence of a cell not only may but 

 must be regarded morphologically as the formation of 

 a new one. 



B. Cell-formation by Conjugation. — The proto- 

 plasmic bodies of two or more cells coalesce to form 

 one common protoplasmic body which surrounds itself 

 with a cell-wall, and becomes endowed with the other 

 properties of a cell. For the elucidation of this process, 

 which presents many variations, we may observe the 

 conjugation of one of our commonest filamentous Algae, 

 Spirogjra longata (Figs. 5, 6). Each filament (Fig. 5) 

 consists of a row of similar cylindrical cells, each of 

 which contains a protoplasm - sac ; this encloses a re- 

 latively large quantity of cell - sap, in the midst of 



which hangs a nucleus, enveloped in a small mass of protoplasm, and attached to 

 the sac by threads of the same substance ; in the sac lies a band of chlorophyll, 

 which is spirally coiled, and at definite places contains grains of starch. In this 

 case the conjugation always takes place between the adjacent cells of two more 

 or less parallel filaments. A preparation is made for it by the formation of lateral 

 protuberances, as represented in Fig. 5, a ; these continue to grow until they 

 meet {b). The protoplasm-sac of each cell concerned then contracts ; it detaches 

 itself sharply from the surrounding cell- wall ; rounds itself into an . ellipsoidal form, 

 and contracts still more by expulsion of the water of the cell-sap. This occurs 

 simultaneously in the two conjugating cells. ' Next the cell-wall opens between the 

 two protuberances (Fig. 6, a), and one of the two ellipsoidal protoplasmic bodies 

 forces itself into the connecting channel thus formed ; it glides slowly through it 

 into the other cell-cavity, and as soon as it touches the protoplasmic body con- 

 tained in it, they coalesce (Fig. 6, a). After complete union (Fig. 6, b) the united 

 body is again ellipsoidal, and scarQely larger than one of the two which compose 

 it ; during the union a contraction has evidently taken place with expulsion of 



Fig. 4. — A, B escape of the swarm-spores 

 of an Oedog^onium ; C one free in motion ; 

 D the same after it has become fixed and 

 has formed the attaching disc ; E escape 

 of the whole protoplasm of a germ -plant of 

 Oedogonium in the form of a swarm-spore 

 (X350). (After Pringsheim, Jahrb. fijr wiss. 

 Bot. I. pi. I.) 



