14 



upon ©nucleated pieces of cell-^. 

 « 

 Scar membranes occur in most plants of which the cytoplasm 

 is found capable of forming- them^, so far as the above described 

 action of the nucleus is made possible. In some other plants it 

 appears that the conditions for wall-formation are not yet ex- 

 hausted with this; at least, according to Klebs, in plasmolyzed 

 cells of Zygnema the influence of light is a further condition 

 for wall-formation. 



Wo have spoken as yet only of the restitution of the wall. 

 Unfortunately, we are imperfectly informed as to the regenera - 

 tion of the livi ng cell elements . The fact tbiit mutilated cells, 

 whose wounds have been healed by a new formation of membrane, 

 can continue growth has been emphasized for different kinds of 

 plants. Since the cells during and after grov/th contain normal 

 protoplasmic quantities,- so far as an estimate allows of any 

 decision, it may be accepted that the mutilated protoplasmic 

 body is capable of a restitutionary grov/th. Nothing has yet 

 been learned as to whether nuclear fragments, as in the case of 

 (17) protozoa, can also grow into normal nuclei, v^Siether mutilated 

 chromatophores, as those of the conjugates, can attain their 

 normal size by growth, whether in mature assimilatory cells, 

 after the removal of some protoplasm and chlorophyll body, all 

 that remains in the cell can be excited to division;- and much 

 more of the same kind. 



2, RESTITUTION OF THE TISSUES 



In the following, those processes of restitution will be 

 discussed, in which the injured cells themselves are not healed, 

 but in which intact cells near the injured ones mfike reparation 

 by growth, eventually also b)& division. At least two cells will 

 therefore take part in the whole process, the one injured and 

 the one making restitution. 



This, the simplest case, is realized in the liverworts; 

 for example, in Marehantia, If the long, unicellular rhizoids 

 are 'out off from youthful parts of the thallus, compensatory 

 hairs are formed, even after a few days, one of the neighboring 

 cells of the trichome base (compare figure 3a) developes into 

 an unicellular hair. The compensatory hair grows out through 

 the oavity of the mutilated one. and from the end of the stump, 

 into the substratum. The lumen of this substitute hair is often 

 noticeably narrower than that of the normal hair. 



Gruber, (Beitr. z. Kenntnis d. Phyz. u. Biol, d. Proto- 

 zoen in place mentioned p. 13) states that in fragments of pro- 

 tozoa, lacking nucleus, incomplete peristomic regions may still 

 develop as a result of an after effect of the nucleus. Accord- 

 ing "fo Balbiana (Houv. rech. exper. sur la merotomie des infus . 

 ciliees Arch.de Microgr, 1891/1892, T. IV, p. 369) an after ef- 

 fect can be demonstrated only in so far, that a constriction is 

 found in those nucleus-free pieces of individuals, which were 

 taken directly before their cell-division. Never, however, does 

 complete cell-division take place; on the contrary, the two 

 halves fuse again. 



p 



To be sure, there are exceptional cases, in which even 



in the dark (Klebs loc. clt,, p. 541) "a formation of cell walls 

 takes place about tJf^ spherical protoplasts. In pure sugar sol- 

 utions I have obseyyed tlh^B 7^T7 rarely, while, on the contrary, 

 in sugar congo r^^ a number of pjrptoplasts in each larger cul- 

 ture of Zyg^/sma 0. wejr/? surrounded wi^h a red cell -wall". 



