8(38 SUMMARY OF CURRENT RESEARCHES RELATING TO 



4. The testa lias protective contrivances, and there is besides an 

 abundant but not thick-walled endosperm. This is the largest of all 

 the grouj^s, and the protective contrivances are very variously dis- 

 played, as in the last. The endosperm-cells contain proteinaceous 

 substances, oil, or starch. 



5. Those with protective contrivances to the testa and a thick- 

 walled endos2)erm. This double protection occurs in only a small 

 number of plants. The walls of the eudosperm-cells are always of 

 considerable thickness, but not so great as in the case of those which 

 depend on this only for protection. 



Lignification of Epidermal Membranes.* — Besides cuticulariza- 

 tion, the change which characterizes epidermal cell-walls in general, 

 the outermost wall may undergo two others ; it may be converted into 

 mucilage, thereby becoming weakened, or it may be rendered firm 

 by the deposition or infiltration of mineral matters. To these well- 

 known transformations of epidermal cells A. Lemaire now adds 

 lignification, hitherto supposed to be confined to internal tissues. 

 For the detection of lignin he uses the useful reagent suggested by 

 Wiesuer, phloroglucin. A section of epidermis is transferred from 

 an alcoholic solution of the agent to hydrochloric acid, when the 

 lignified membranes assume a rose colour, the other parts remaining 

 unchanged. For purposes of control, similar sections are first treated 

 with either nitric acid or a solution of bleaching powder, by which 

 reagents, preferably the latter, the liguin is removed. Lemaire has 

 detected liguin in the epidermal walls of Cycadefe, many Coniferse, and 

 in the petiole of certain ferns. The stomata of Coniferse and Cycadefe 

 have been found by him always to have the membranes somewhat 

 lignified. 



Protective Sheath and its Strengthenings. f — A further careful 

 examination of this subject leads S. Schwendener to the general con- 

 clusion that a natural classification of tissues must be founded entirely 

 on their structure and function, and not on the variable phenomena of 

 the history of their development. 



Laticiferous Tubes.J — :According to G. Haberlandt, sections 

 through the lamina of thick-leaved species of Euphorbia (such 

 as E. Lathjris, Mijrsinites, or higlandulosa) show that the anatomical 

 connection between the palisade-layer and the laticiferous tubes is as 

 close as between the palisade layer and the parenchymatous sheath of 

 the vascular bundle, and the connection is close in jiroportion to the 

 looseness of the palisade-tissue. Tiie conduction of the products of 

 assimilation takes place, as a rule, by means of funnel-shaped or spongy 

 parenchymatous cells. In the thin-leaved species such a mode would 

 be superfluous. Where the laticiferous tubes are found on the upper 

 boundary of the palisade-layer beneath the epidermis, the palisade- 



* Ann. Sci. Nat., xv. (1883) pp. 297-302. Cf. Science, ii. (1883) pp. 112-3. 



t Abhaudl. K. Akad. Wiss. Berlin, 1882, 75 pp., 5 pis. Cf. this Journal, mite, 

 p. 679. 



X SB. Akad. Wiss. Wien, Ixxxvii. (1883) (2 pis.). See Bot. Centralbl., 

 XV. (1883) p. 35. 



