260 Scott and Brebner . — On Internal Phloem 
of Russow 1 , Vesque 2 , Petersen 3 , and Solereder 4 , we are now 
able to form a fair estimate of the distribution of this character 
among the dicotyledonous orders, though it is almost certain 
that additions will still be made to the number of those which 
possess it. Taking Solereder’s summary 5 as the latest avail- 
able, we find bicollateral bundles in the following orders : 
Polypetalae\ Vochysiaceae,Melastomaceae, Myrtaceae, Lythra- 
ceae, Onagraceae, Cucurbitaceae ; also in some Combretaceae. 
Gamopetalae : Asclepiadaceae, Apocynaceae, Solanaceae, Genti- 
aneae, Loganiaceae ; also in most Convolvulaceae, and in some 
Acanthaceae. Apetalae\ Thymelaeceae, Penaeaceae, Euphorbi- 
aceae (sub. tribe Eu-crotoneae, &c.), and in one genus of Poly- 
gonaceae. In the great majority of these eighteen orders, the 
character is constant throughout, with the occasional excep- 
tion of a divergent tribe. For the systematic details Solere- 
der’s work must be consulted. We have not included the 
Cichoriaceae and Campanulaceae, in which the nature of 
the medullary vascular tissues is open to some doubt. 
Enough has been said to show that bicollaterality is a char- 
acter widely prevalent among the most highly organized dico- 
tyledonous families and of great systematic value. It may 
fairly be maintained, that these orders represent, in certain 
directions, the most advanced types of dicotyledonous structure. 
1 Betrachtungen liber das Leitbiindel- nnd Grundgewebe ; Dorpat, 1875. 
2 Anatomie comparee de Tecorce ; Annales des Sciences Nat., Bot. Ser. 6, T. II. 
1875. 
3 Ueber das Auftreten bicollateraler Gefassbundel ; Engler’s Jahrbuch fur Sys- 
tematic, Bd. III. 1882. 
4 Ueber den systematiscben Werth der Holzstructur bei den Dicotyledonen ; 
Munich. 1885.' 
5 Loc. cit., p. 28. We are not aware of any additions to the list since, unless it 
be the Basellaceae, a family of climbers allied to the Chenopodiaceae, investigated 
by Morot and not mentioned by Solereder ; see Morot : Note sur 1’ Anatomie des 
Basellacees, Bulletin de la Soc. Bot. de France, vol. 31, 1884. Medullary phloem, 
accompanied by xylem, has further been found by Dangeard in Acanthophyllum 
(Caryophyllaceae) ; by Robinson in lodes (Phytocreneae), and by ourselves in 
Acantholimon (Plumbagineae) ; but these formations are allied rather to those in 
the pith of Tecoma than to the internal phloem of bicollateral bundles : see 
Dangeard, Monographic anatomique des Acanthophyllum, Le Botaniste, 1889, 
p. 194; Robinson, on the stem-structure of lodes foment diet, &c., Annales du 
Jardin botanique de Buitenzorg, vol. VIII. p. 95, 1890. 
