212 r in'n rsil !i of (\il ifoniid I'lihlicdl laiis in lloidiiii | N'm,. 7 



Toiidors iiinvo simple tlic lijiiidliiii;' of Ihc iiii|Hit't;iii1 l)tii'ky clenieiits. 

 The ad ii;il cross srcl ions jii'c iii.kIc with ;i sectioJi kiiifi' or h<';i vy-hnckcd 

 I'lizoi" iiol hoMow Lirouiid. 'The piece of iiuiterird may he h''hl in the 

 iiiij^'crs i'oi' ciiltiii^ or in a so-caUed hand oi' well microtome. One of 

 lis lias devised a modification of this 1\'pe of ndcrotome which was 

 nsed in these investijiations.'" A slidin<i' microtome has also hecii nsi'd. 

 Successful sections can he cut only with an extremely sharp instrument 

 and only a few sections can he cut heforc sliar])eninf; must he repeated. 

 Smoothing' the surface to he cut with a sluiip ])Ocket knife is desirable 

 and saves toi- a lime the liner edge of the sectioning razor. 11' interest 

 centers enlii'ely upon the (piestion of the pri'sence or absence of rubber, 

 it is not essential that the sections cut he paiiicuhirlx- thin nor that 

 they he taken exactly at right angles to the long axis of the sample. In 

 our work details of structui'e and other matters were often of special 

 im])ortance for which reason nW sections were cut less than .lO/j, in 

 thickness and were carefully oriented. 



As noted by Lloyd^* rubber when jireseut in large amount is. after 

 some practice, rather readily detected in fresh or unstained sections 

 of non-latex rtd^her ])lants. When present in smallei- quantities it is 

 often indistinguishable fi'om the protoi)lasmic matrix of the cell or is 

 confused with accumulations of oil or resin in the tissues. According 

 to oui- histological method oils and resins were dissolved out because of 

 tlie i-elatively small amount of ruhhcr usually present and especially 

 as a j)reliminary to the use of a stain which was not definitive for 

 rubber i]i the pi-esence of these other sid)stances. As a solvent, acetone 

 was used exclusive]}', the sections being placed in a test tube half full 

 of acetone and allowed to stand in a water bath at 60° C. for from 

 fifteen to thii-ty minutes. For staining the sections we at first tried 

 alkanin,'-' hut Sudan III was early found to be more satisfactory and 

 was therefore employed in the great majority of the histological exam- 

 inations. Our Sudan TTT was made \\\) with glyceiine according to 

 Stevens' fonnula."' This stain imparts a brilliant seai'let coloi- to fats. 

 iTsins and i-uhbers as they occur in the cell. Wy the ])revious acetone 

 extraction fats and resins had been dissolved fi'oni the cell contents 

 hut rublxM- was left ])ractically uiuiffected and if i)i'csent took up the 

 stain. The stain was allowed to act for eic-htecn hours, after which the 



'•'' (t()()ils]><'<i|, T. ]I.. Modification ol' liaml iiiiciotdiiic liot. (iaz., vol. ()(> 

 (1918), p. 5:54. 



i-t Lloyd, F. E., Giiayulr. Canicoi,. Inst. I'lil.l. no. I .S9 (1911). y. 17(!. 



i-^'Cf. Stevens, \V. (\. Plant anatom.v. i'.d cd. (191(;). p. 29:!. 



!'•• L.C., ]). .*}:57. 



