36 



Fig. 20 h shows a transverse section of a part of a thallus in 

 which the cells have just been divided in this way. We see that 

 the wall of the mother-cell (marked x in the figure) covers over 

 the young cells and, further, we find that at each two — three or 

 four cells the cross walls of the mother cells (marked y in the 

 figure) run in between the daughter cells. On the exposed outer- 

 side or on the upperside of the flat old thallus the wall of the old 

 cells seems soon to be torn off; on the other hand, in the thallus 

 still in the form of hollow sacs we often find several layers of old 

 membrane covering the sheltered innerside. 



The cell-division does not take place simultaneously in all 

 cells of the thallus ; we often find, on the contrary, that it is only 

 a group of cells here and there which is divided, sometimes also 

 a single cell only has been divided. Fig. 20 a shows a part of an 

 old thallus with divided and not divided cells. 



I have mentioned above that the young unicellular speci- 

 mens might perhaps have their origin from aplanospores. I 

 think it very likely namely, that the above-mentioned balls, 

 formed by the cell division, may occasionally become free and 

 be able to grow to new plants. 



In the quite young small plants the thallus is massive (Fig. 

 20 c) but by cell-division the cell layer in the periphery will grow 

 larger and larger, first making the thallus sack-shaped (Fig. 19) 

 and at last it will be torn (Fig. 22) and disc-shaped. These old 

 disc-shaped specimens can be very large ; I have collected speci- 

 mens with a diameter of about 12 cm. 



As to the hapterse found along the edges of the cells, these 

 all grow out from quite small cells which are very similar to the 

 small lentiform cells found in Valonia^). These small cells are 

 arranged in series (most often 3) along the edges of the large ones 

 (Fig. 21 d) and very regularly, alternately opposite each other in 

 such a way that the hapterse growing out from the small cells 

 attach themselves to the wall of the neighbour cell just in the 

 intervals between the small cells on it (Fig. 21 e, /). In this way 

 the large cells are very firmly fixed together. The small cells are, 

 when seen from above, oval oblong, sometimes also quite circular. 

 One to two haptera) grow out from them (Fig. 21 d. e). 



The small cells also occur abundantly upon the sack-like 



1) It has been of interest to me to see what Heydrich writes about this 

 matter; p. 468 (I.e.) he says: »Jede Fibula bildet an der Stelle, wo 

 sie der Wand der sie erzeugenden Zelle ansitzt, eine uhrglasformige 

 Vertiefung«. 



