ROT ALIA. 



[ 668 ] 



ROTATION. 



matous tissue, in which the cells are cha- 

 racterized by delicate open spiral-fibrous 

 secondary layers. 



Roots grow by cell-development only near 

 the apex; and interstitial expansion soon 

 ceases. Old roots of Dicotyledons present 

 a dense heart-wood like the trunks, the 

 passage of fluid taking place through the 

 outer layers. When the older parts of roots 

 are exposed to the air by removal of soil, 

 they acquire a thick corky periderm. The 

 general structure of the root of Conifers is 

 like that of Dicotyledons. 



BIBL. Henfrey-Masters, Bot. ; Nageli and 

 Leitgeb, Nag., Wiss. Sot. 1867 ; Hofmeister, 

 Morphol. d. Geweb. 1865 ; Tieghem, Ann. 

 Sc. N. 5. xiii.; Sachs, Sot. 165; Olivier, 

 Rac. Ug. 1882 (50 pis.). 



ROTA 'LI A, Lamarck (restricted). A 

 typical Foraminifer; shell ammoniform, 

 neat, finely porous, unequally biconvex ; 

 with 13-40 chambers, double . septa, and 

 canal-system ; limbate and often granulate. 



Species numerous, both fossil and recent 

 (R. Beccarii, PI. 24. figs. 13, 14). 



BIBL. Carpenter, For. 212; Micr. 546; 

 Parker & Jones, Phil. Tr. civ. 387. 



ROTALI'NA, Carpenter (Rotalina). 

 A subfamily of Globigerinida. See FORA- 



MINIFEBA. 



BIBL. Carpenter, For. 198; Parker & 

 Jones, Phil. Tr. civ. 378, and Qu. J. G. S. 

 xxxviii. 103. 



ROTATION or C YCLOSIS. This term 

 is usually employed in botanical works to 

 denote peculiar flowing movements of the 

 contents of vegetable cells ; and it is useful 

 to retain the word for all cases of the kind, 

 in order to avoid confusion of these pheno- 

 mena with the general circulation of the sap. 

 The term " circulation of the cell- sap " is, 

 however, often used instead of rotation, and 

 especially in reference to the cases where it 

 exnibits numerous distinct currents. 



The rotation presents itself in two types, 

 namely (1) a rotatory movement of a layer 

 of protoplasm investing the entire internal 

 surface of the cell, as in CHARA, &c. ; and 

 (2) a radiating movement of the protoplasm 

 in slender currents, from the nucleus out over 

 the remainder of the cell, with a return flow 

 towards the nucleus ; but as the nucleus 

 itself shifts in the latter type as in the 

 former, the two kinds are scarcely definitely 

 distinguishable ; they may, however, be 

 spoken of separately. 



The rotation in Char a and NiteUa has 

 been long known ; a similar movement oc- 



curs in many water-plants, such as Vallis- 

 neria, Hydrocharis, Anacharis, Slratiotes, 

 Sagittaria, Potamoffeton,Ceratophi/llton, &c., 

 where it is seen best in the more delicate 

 foliaceous structures, such as young leaves, 

 stipules, or sepals, or in the young rootlets. 

 It has also been observed in the fruit- stalks 

 of Slasia pusilla and some other Hepaticse. 



In the CHAEACE^E the wall of the cells is 

 lined with chlorophyll-granules, leaving two 

 oblique or spiral stri8e bare (fig. 125, p. 162) ; 

 these striae indicate the boundaries of the 

 ascending and descending currents (marked 

 by arrows) . The moving substance is a vis- 

 cid semifluid layer, lying within the chloro- 

 phyll-layer, and itself surrounding the 

 watery cell-sap occupying the centre of the 

 cell. This layer, forming a kind of gelatinous 

 sac, moves in a spiral course up one side of 

 the cell and down the other, the motion 

 being rendered very evident by chlorophyll- 

 and other granules imbedded in it ; these 

 appear to be carried along passively by the 

 stream, the larger slowly, the smaller with 

 greater rapidity. In VaUisneria, Anacharis, 

 &c. the chlorophyll-granules and the nu- 

 cleus are imbedded in and moved with the 

 flowing protoplasm. If long cells of Chara 

 are bent or tied round by a ligature, the 

 circulation is not stopped, but takes place 

 independently in each half. If a cell of 

 Chara is cut across, the protoplasm of the 

 current flowing towards the cut surface 

 escapes at once, but that of the current 

 flowing away, goes on to the end of the 

 cell, turns round, and then flows towards 

 and out from the wound. 



The size of the stream seems to be in in- 

 verse proportion to the length of the cell, 

 decreasing as the latter acquires its full 

 development. The rapidity of the current 

 varies according to the age of the plant and 

 the activity of its vegetation. It is most 

 rapid in hot weather and in sunshine. Arti- 

 ficial elevation of temperature in the water 

 in which the plant grows, up to a certain 

 point, hastens the movement; a heat above 

 80* Fahr., however, retards it for a time. 

 A temperature of 112 Fahr. kills the plant, 

 as also does a cold of about 20. Darkness 

 appears merely to exert effect through its 

 influence on the activity of the vegetation. 

 Keeping Chara in water exhausted of air 

 does not stop the rotation until the plant 

 dies. Most chemical reagents seem to exert 

 no special action ; only lime-water appears 

 to stop it in a few moments. A solution of 

 sugar, or gum, or milk greatly hastens the 



