742 
Lee. — Observations on the 
cotyledons were petiolate, retuse, and markedly unequal. A number of 
small veins supplied the lamina, and these were collected at the base into 
a single bundle which entered the petiole. The transition, slightly obscured 
by the presence of secondary thickening in the hypocotyl, was of Type 3, 
and began in the petiole. In the shorter petiole, the protoxylem became 
external by simple rearrangement of the xylem elements. In the other the 
xylem divided into three portions, the median one (protoxylem) taking up 
an external position. The metaxylem in both cases moved towards the 
centre, became fragmentary, and finally disappeared, leaving only the 
protoxylem groups of the original cotyledonary xylem strands. These 
gradually closed in, and with the reappearance of the metaxylem a small 
diarch plate was produced. 
Acanthaceae. 
The only member of this order of which the seedling anatomy is 
known is Acanthus , which was investigated by Dangeard ( 5 ). The transi- 
tion is essentially the same as in the Scrophulariaceae. 
Theoretical Considerations. 
On the present occasion it is not proposed to give a full discussion of 
the bearing of the above observations on the various phylogenetic theories. 
Quite recently, in discussing the theoretical importance of the seedling 
structure of the Cactaceae, de Fraine (6, p. 164) gave a summary of the 
principal theories based on, or influenced by, the seedling anatomy, which it 
is hardly necessary to repeat here. Briefly, the observations on the Tubi- 
florae entirely support the general conclusions of that author. 
In the Tubiflorae examined there are two fairly well marked methods 
of transition : 
(1) Characterized by possession of a diarch root throughout. This 
method, known as Van Tieghem s Type 3, has been found in the 
majority of the plants investigated, e. g. Polemoniaceae, Hydro- 
phyllaceae, Boraginaceae, Labiatae, Solanaceae, Scrophulariaceae, 
some Bignoniaceae, and Acanthaceae. 
(2) In which the root is tetrarch in structure. These can be further 
classified according to the number of bundles in the upper part of 
the hypocotyl. 
(a) In the Convolvulaceae, a ‘double’ midrib and two small lateral 
bundles enter the hypocotyl from each cotyledon and become orientated to 
produce the tetrarch root. This is obviously merely a modification of 
Van Tieghem’s Type 2. 
(b) In some Bignoniaceae (e. g. Incarvillea Delay vei ) a single bundle 
enters the hypocotyl from each cotyledon, where it undergoes division and 
orientation which result in the production of a tetrarch root structure. 
