SECONDARY DEPOSITS. [ 687 ] SECRETING ORGANS. 



Pinus, &c. The membranes forming the 

 sheaths of many of the Oscillatoriacese 

 (PI. 8. figs. 13 d, e, 16) exhibit a spiral- 

 fibrous structure when undergoing dissolu- 

 tion ; and an analogous condition may be 

 detected by the help of reagents pretty 

 generally in the cell-walls of the tubular 

 Confervse. All these phenomena seem to 

 indicate a fundamental identity in secon- 

 dary layers of all kinds, to which we direct 

 attention under SPIRAL STRUCTURES ; but 

 it is convenient to keep the PITTED and 

 SpiRAL-fibrous structures distinct. 



The mode of formation of the secondary 

 deposits is not clearly known : some imagine 

 them to be precipitated from the cell-sap 

 upon the walls ; others, and apparently with 

 more reason, believe that they are attributable 

 to the agency of the PRIMORDIAL UTRICLE, 

 continuing its action after the formation of 

 the primary membrane. Criiger goes so far 

 as to consider the spiral markings, &c. as 

 dependent on the RoTATiON-currents of the 

 protoplasm. There can be little doubt of 

 the mistaken character of Trecul's view, 

 which regards the spiral and other fibrous 

 thickenings as folds of the primary wall 

 thrown inwards. 



The secondary deposits appear to be always 

 composed of some modification of cellulose. 

 Mohl has investigated this point very 

 thoroughly ; and we have followed him over 

 much of the ground. The cellulose, how- 

 ever, loses its distinctive character with 

 age, either by infiltration with foreign 

 matters, or by a slight chemical metamor- 

 phosis, so that old secondary layers do not 

 readily become blue when sulphuric acid 

 and iodine are applied; but as a general 

 rule the cellulose reaction may be obtained 

 by using a preliminary treatment. All in- 

 ternal structures, such as wood-cells, liber- 

 cells, stones of fruits, &c., should be boiled 

 in nitric acid, washed, dried, and tincture of 

 iodine applied; then, if again dried and 

 wetted with water, they turn blue. Ex- 

 ternal structures, such as epidermal cells, 

 cork, and the like, require boiling with solu- 

 tion of potash. 



Secondary deposits present considerable 

 difference in their consistence and degree of 

 development in different cases. In most 

 wood- and liber-cells they are abundant in 

 quantity, in some cases almost filling up 

 the cavity (PI. 47. fig. 27) ; here they are 

 hard, and! appear to be in that state of the 

 cellulose-compound which may be distin- 

 guished as lignim. The same condition 



prevails in the stones of fruits, bony shells, 

 the gritty tissue of pears, &c. j and the less 

 abundant secondary substance of spiral- 

 fibrous tissues appears to be in the same 

 state. The secondary layers of parenchy- 

 matous cells are usually rather soft and 

 elastic, and often turn blue with sulphuric 

 acid and iodine alone ; those of the collen- 

 chymatous tissue beneath the epidermis of 

 many herbaceous plants, such as the Che- 

 nopodiaceae, &c., are abundant in quantity, 

 but of somewhat cartilaginous texture. 

 Those of the larger Algae, and of the thallus 

 of the larger Lichens, approach to the same 

 condition, while the fleshy and horny AL- 

 BUMEN of many seeds contains abundant 

 deposits of analogous character (PI. 47. 

 figs. 21-23) ; in the latter the composition 

 is sometimes of amyloid, approaching starch, 

 stained blue by iodine alone, and more or 

 less soluble in dilute sulphuric acid. The 

 secondary layer of epidermis and corky layers 

 differs again, being usually more sparing in 

 quantity, but very firm and elastic, and 

 strongly resisting decomposing agents ; the 

 composition appears to be of that modifica- 

 tion of cellulose called suberine. 



BIBL. Mohl, Vegetable Cell, 1852, Hot. 

 Zeit. 1847, 97, Taylor's Scientific Memoirs, 2. 

 i. 95 ; Schacht, Pflanzenzelle, 1852 ; Criiger, 

 JBot . Zeit. xiii. 1855, 601 ; Trecul, Ann. Sc. 

 Nat. 4. ii. 273 ; Wigand, IntercelMar-sub- 

 stanz, 1850 ; Mulder, Phys. Chem. ; Henfrey- 

 Masters, Bot. 



SECRETING ORGANS OF PLANTS; 

 RESERVOIRS OR RECEPTACLES for SECRE- 

 TIONS. The structures falling under this 

 head have been in part treated of under the 

 heads of GLANDS and LATICIFEROUS TIS- 

 SUE ; but there still remain certain organs 

 of analogous character, which could not be 

 properly included under either of the above. 

 The name of receptacle or reservoir for 

 peculiar secretions is ordinarily applied to 

 groups of cells, of variable, but most fre- 

 quently elongated prismatic form, contain- 

 ing special secretions, either in their ca- 

 vities or effused into their intercellular 

 passages, traversing in the form of cords or 

 bundles the parenchymatous or prosenchy- 

 matous tissues. They are almost special 

 characteristics of families, and by no means 

 frequent; the Coniferae, the Cycadacea3,the 

 Aloineous Liliacese, the Polygonaceaa, Com- 

 positae, Umbelliferae, Amygdaleous Rosacese, 

 Leguminosae, &c. afford striking examples. 



In the Coniferae the turpentine-reservoirs 

 are very remarkable ; and to a certain extent 



