660 SUMMARY or CURRENT RESEARCHES RELATING TO 



than that of N. major. Here there are one or two axile vessels separated 

 from the encloderm by a single row of cells in which are 3-4 sieve- 

 tubes. The central cylinder of the root of N. minor and of N. major is 

 therefore but very slightly lignified, and corresponds to a single bundle 

 with an axile vessel representing the xylem and peripheric phloem. 



The author then describes the structure of the root of several species 

 of Potamogeton. In P. natans not only can the endoderm thicken its 

 cells either on their outer or on their internal and radial faces, but 

 the permeable places are frequently wanting. All the elements of the 

 central cylinder are susceptible of thickening or lignifying, the sieve- 

 tubes only being an exception. Every species of Potamogeton studied 

 by the author possessed true vessels, and several possessed sclerenchy- 

 matous tissue to a greater or less extent. When the sclerenchyme was 

 feeble, it showed in the endodermal cells opposite the liber. 



M. Sauvageau next describes the mechanical system in the roots of 

 Zostera, Cymodocea, and Posidonia. The anatomy of these plants differs 

 very considerably, Zostera and Cym,odocea possessing no lignified elements 

 in their roots, while Posidonia Caulini, which is deeply submerged, 

 possesses on the contrary a ligneous conducting system and an im- 

 portant sclerotized mechanical system, which renders the root hard, and 

 gives to it a considerable power of fixation. Comparative anatomy has 

 shown that aerial roots when they become subterranean, or subterranean 

 roots when they become submerged in water, lose either in part or 

 altogether the property of thickening, and especially of lignifying their 

 cell-walls; but this conclusion is due in certain cases to a sickly 

 condition of the roots, which is a result of their existence in a different 

 medium from that for which they were adapted. 



Comparative Anatomy of the AristolocMacese.* — Dr. H. Solereder 

 describes the various points of anatomical structure in this order, 

 especially in relation to the leaves, the vascular bundles, the fruit, and 

 the seeds. Secretion-cells occur throughout the order, and in almost all 

 the species they are found in the lamina of the leaf, in the epidermal 

 tissue as well as in the mesophyll. They may occur in the epiderm of 

 both surfaces, or in that of the under surface only ; their walls are very 

 often suberized ; their contents are in the form of yellowish or whitish 

 drops. When occurring in the leaf, they are to be found also in the 

 flower. The pollen-grains are always spherical, with neither fissures nor 

 pores. 



Structure of Apocynacese-t— According to M. Garcin, plants 

 belonging to this order are characterized by the presence of a double 

 liber in the stem, an outer and an inner portion, and by the occurrence 

 of unseptated laticiferous tubes, and of a pericycle inclosing bundles of 

 fibres with thick walls composed of cellulose. The same essential 

 characteristics occur also in the Asclepiadeae. 



Anatomy of Dioscoreacese.^ — From the examination of a number of 

 species belonging to this order, Herr J. E. Jungner describes the 



* Engler's Bot. Jahrb., x. (1888-9) pp. 410-524 (3 pis.). See Bot. Oentralbl., 

 xxxviii. (1889) p. 8.55. 



t Ann. Boc. Bot. Lyon, xv. See Morot's Journ, de Bot., Rev. Bibl., iii. (1889) 

 p. xliii. 



X Bih. K. Svcnfck. Vct.-Akad. Handl., xiii. (1888) Afd. 3, No. 7. See Bot. 

 CentralM., xxxviii. (1889) pp. 734 and 760. 



