44 



THE CAUSES OF FLUCTUATIONS IN TUEGESCENCE 



simplest form, it is advisable to study it somewhat closely ere proceeding to the 

 consideration of cases in which the movements are no longer determined by the mutual 



relations of individual cells, but by those of complicated masses of tissue. 



A 



every 



one is aware, the 

 that, under certain 

 water, the guard-ce 



opening 

 condit 



and closure of the stomatic orifices are due to the fact 



of illumination 



pp!y 



d transpiratory loss of 



become so turgid that they are able to deter 



a certain 



amount of displacement of the surrounding epidermal 

 of these conditions, they lose turgidity to a gi 

 able to withstand the recoil of the 



their 



elements; and that, in the absence 

 or less degree, and, being no longer 

 hbouring tissue, they allow it to approximate 

 inner surfaces and more or less completely to close the interspace between them. 

 This, it is evident, implies that under favourable conditions the guard-cells become 

 more turgescent and, for the time being, stronger than the other epidermal elements; 

 for did they not do so displacement of the latter would be impossible. We have then 



in the first pi 



to ascertain what are the distinctive features 



compared with the other epidermal elements, which 



the guard 



as 



ated with 



pa city for 



temporary increase in strength. And when we have done so we find them to be the 

 following :— 1st, they are 



younger than then* 



ghb 



protoplasm; 3rd, they are conspicuous as containing a relative a bund 

 phyll ai 



2nd, they are richer in 



d 



starch; m, they are, as Kienitz-Gerloff 



fact that there is no continuity between their protoplasm and that 



mce of chloro- 

 has shown.* distinguished by the 



cells. The three first of these charactei 

 nyctitropic tissues generally; but the fou 

 ments are determined, not by alteration 

 masses of tissue. In the case of th 

 ing for tl 



we find tl 

 of 



f 



neig 



hbo 



in 



are characteristic of the active elements 

 i is naturally absent in cases where move 



in th 



turg 



guard-cells it is necessary 



of isolated cells, but of 



conditions provid 



excessive turgidity of individual cells should be provided, and accordingly 

 cell-cavihes closed and the protoplasts isolated: but in the «. „f «.-ul 



tissue thei 



ed and the protoplasts isolated 



the individual units 



would, of course, be no 



in the case of masses 



That th 



ing mto their constitution. 



dvantage attained by the isolation of 



guard-cells belong to a 



., . „ younger generation than the 



inon epidermal cells is a well-recognised fact. 



version of Sach 



Text-book of Botany 



In the first edit 



ding com 



» 



f the 



English 



not arise until rather late, that 

 and leaves, their « 



is, during 



. arran genient is partly dependent on the 

 ot the epidermis cells," and that " 



we find it stated that " as the stomata do 

 or after the expansion of the 



the formation of a mother 



the origin of the 



stomata 



fir 



is 



6 



vhich 



pide n 



iard-< 

 It 



of all 



division of a 



is sometimes preceded by several preparatory divisio 



internodes 

 ally elongated form 

 always the result of 



pidermis cell, 



young 



cells ; 



d this mother 



in it or in adj 



are formed from it by division." f 



becomes more and more rounded off 



d the 



is 



unnecessary to quote an} 



pecial authority for the 



dance of protoplasm, and particularly of chlorophyll 



fa 



of the 



as compared with oth 

 casual ob 



epidermal element 



as it is one 



and starch 

 svhich is e 



pecial 



in the guard -cells 

 ident to the most 



* 



Die ProtoplasmaTerbiadungeu z«i sc hen benachbartea 



Bot. Zeit. 1891. 

 t A Text-book 



GewebeseWntea der Pflanze. 



F. Kiemtz-Gelloff 



Sacbs. Bennett and Dyer, 1st ed., pp. 75, 



87. 



