62 



two vtreak*conc.entration or of unsuitable composition . 



The above mentioned process of growtli in thickness can be 

 corabined also with changes in growth of the whole cell., That 

 is true of the netted--d^^ct thickenings first named, as well as 

 of the irregular cellulose accumu^-ations free from bordered 

 pits, \7e will have to return therefore in the next chapter to 

 similar structures. 



Changes in the ehemical composition of . the membrane as 

 well as pathological changes of the cells, micro -chemically 

 demimstrable, do not belong to our suhject. Besides it is not 

 improbable, that, just as in the formation of abnormal _ eel lu-._ 

 lose deposits, processes of a degenerative nature are involved 

 in the production of foreign matters, which impregnate the cell- 

 ulose covering and change thereby the chemical character of the 

 cell wall-. In any case the death of the cell often follows. 

 Some few notes on suberization and lignification suffice here.. 



In the case of rhizomes and petiole of some ferns,, a 

 Vrowning of the cell-wall follov7S an injury, which makes ItsaXf 

 evident first in the middle cells, then also in the other lay- 

 ers of the cell' wall. Retiention in water appears, in higher ^ 

 plants, to cause the sTiberization of the superficial tissues ,, 

 According to Tittman"^ the exposed cross walls of the cut hyphae 

 of Cladojihora glom e rata , develop a cuticle. 



I. observed lignification of the cell walls without notice- 

 able grov;th in thickness in the leaves of Juglans under the in- 

 fluence of colonies of Lachnus Juglandis . The 16af lice stayed 

 on the upper side of the leaves, in fact on the mid rib, and 

 brought the tissue lying over the rib to lignification. Simi- 

 lar effects might also he caused by other parasites which do 

 n«it.. form galls , 



^ Compare for instance, Dassonville, Jnfl^.des sels miner- 

 aux sur la forme et la struct-^ des veg. Rev. gen..de Bot. 1896, 

 T. VIII, p. 284; Pethybridge, loc. , cit . Further, Stange , Be- 

 zieh. zwisoh. Substratconcentration.. Turgor u. WachstTim bei 

 einigen phanerog, Pfl. Botan. , Ztg. 1^92, Bel. L, -• 365. 



^ According to Costantin, Etude comt). d. . tiges aerienhes et 

 souterraines des Moot. Ann. So. Hat;, .Bot ,, .1883, 6™^ s^r.,_T. 

 ZVI, p. 4; also Rech, s. la struct; de la tige d. pi* aquatiques, 

 Ibid, 1884, 6^6 ser., T, XIX, p. 287. Sapvageau observed th&t 

 in aquatic plants Potamoge ton and others, the cells lining the 

 air passage turned to cork after the intercellular space,s had 

 been filled with water. ^ fSux les feuilles de quelqu. monocotyl^d, 

 aquatiques. Th^se, Paris 1891, p. 181). According to Thomas. J. 

 (Anat. comp. et exper. d. feuilles souterraines. Rev. gen. de 

 Bot., 1900, T. XII, p. 394) the cuticle of the under side of the 

 leaf is more conspicuous in the cultivation of shoots bearing^ 

 leaves under the surface of the ground than under normal condi- 

 tions,, • 

 ;.@x.. 



^ Beob. uhA Bildung u. Regeneration d. Periderms, d. 

 Epidermis, d. #fhsuberzuges . etc. Pringsheim^s Jahrb. f. wiss . 

 Bot., 1897, Bd^ XXX^ p. 116. 



^ Kochs /loc. eid.) observed lignification (metaplasia) in' 

 twigs infected by Asterodiaspis quercicQla; ( Coccus Quercus ) . 

 Part of the ^ark cells grovif~^6atiy in; a tadial direction and 

 lignify later - others turn to wood^ without any previous elon- 

 gation. 



