326 Sampson . — The Morphology of 
doubtless connected with the need for a more abundant water-supply. 
The more primitive features of the tuber would not be looked for in the 
long shaft of the tuber, which is clearly an adaptation to a geophytic 
habit, but in that part of the tuber most closely connected with the 
main axis. Such features have already been found in the origin of the 
tuber stele, and others will be dealt with in the following section. 
c. Leaves connected with the New Tuber. 
Mettenius, in his memoir of Phylloglossum , describes a small tongue- 
shaped body, frequently found above the new tuber. This structure he 
regards as an atrophied leaf, since, in his material, it was connected by 
transitional forms with the normal leaves of the plant. 1 A similar body 
was observed by Bertrand, and named the ‘ organe de Mettenius but his 
material showed none of the stages which led Mettenius to his conclusion. 2 
Bower, however, states that, in several of the mature plants he examined, 
a leaf placed above the new tuber was frequently smaller than the others, 
and he suggests that it corresponds to those structures observed in a similar 
position by earlier writers. 3 
The aim of this section of the paper is twofold ; in the first place, to 
confirm the work of Mettenius by showing that the organ which bears his 
name is indeed a reduced leaf, and, secondly, to show how some of the 
lower leaves of the plant are connected with the new tuber. 
The general structure of the tuber, the bud of which is sunk at the 
base of a narrow channel, has already been described (p. 317). The mouth 
of this channel is situated on the outer surface of the tuber, often at the 
base of a small hump of tissue borne in the angle between the new tuber 
and the peduncle of the cone. In some cases this hump of tissue can only 
be observed in a microscopic examination (Fig. 4, B, rdf in others it may 
be seen with the naked eye or with a lens, and recalls then the tongue- 
shaped body described by Mettenius and Bertrand (Fig. 2, rd.). A vascular 
supply is generally found, consisting of a slender strand of tracheides, which 
dies out before the tip of the organ is reached (Fig. 5, sect. 1, rd,, and 
Fig. 3, sect. 1). Occasionally, in place of this tongue-shaped structure 
a small but otherwise normal leaf is found, the ‘ supernumerary leaf’ of 
Professor Bower. Such a leaf is shown in Fig. 2, a, sd ., and appears in 
section in Fig. 3, sect. 1. A complete series of transitional forms connects 
such leaves with the various structures described above, and there is 
no doubt that all are merely stages in the reduction of one of the normal 
leaves of the plant. 
1 Mettenius : loc. cit., P.-99. 2 Bertrand: loc. cit. , 1885. 
3 Bower : loc. cit., 1886, p. 670. 
