Vascular Anatomy of Tubers of Nephrolepis. 73 
Descriptive. 
Several species of Nephrolepis 1 are now known to possess 
tubers, which are as a rule terminal swellings of short branches of 
the underground 2 stolons. The apex of the branch forms a minute 
mamelon at the distal end of the tuber. Only rarely, according to 
Professor Goebel’s observations, 3 is the mamelon developed into a 
stolon while the tuber is still attached. The tuber is so completely 
protected by imbricating peltate scales that no part of its surface 
is left exposed. The fresh tubers examined by me contained enough 
sugar to give them a sweetish taste, and a copious brown precipitate 
with Fehling’s solution confirmed the presence of a considerable 
quantity of a reducing substance. The outermost one or two layers 
of cells also contained a few starch-grains. 
Pig. 1, A, illustrates the vascular relations between the stolon 
and the tuber. We shall follow the transition from the solid 
protostele of the stolon to the netlike stele of the tuber, as revealed 
by a series of transverse sections from the base upwards. But 
before describing these changes it will save some repetition to state 
that the manner in which the strands finally fuse up into the solid 
protostele at the apex is the reverse of the process of disintegration 
occurring at the base. In both these processes, however, individual 
variations are met with, which we shall later attempt to explain. 
The strand of the branch-stolon penetrates the base of the tuber 
as a solid protostele for a few millimetres; its four or five 
protoxylems, hitherto more or less clearly seen, 4 may at this time 
become indistinct. The xylem then begins to dilate in a funnel-like 
manner and acquires a central mass of phloem which enlarges and 
is soon followed by pericyle, endodermis and ground-tissue in 
succession. The solid cylinder of xylem has been converted into a 
1 Heinricher, loc. cit., p. 67. Tubers have also been recorded in N. neglcctn 
by Lachmann. “ Recherches sur la morphologie et l’anatomie des fougeres,” 
(Comptes rendus, Cl, 1885, p. 605), and in N. undulata by Kunze (Hot. Ztg., 
1849, p. 882) and by Hofmeister, {loc. cit., p. 65); but these species may be 
synonymous with some of those mentioned by Heinricher. 
3 Under certain conditions, according to Sperlich (Flora, 1906, p. 454), 
tubers may be produced on the aerial stolons. 
* Goebel, K., “ Pflanzenbiologische Schilderungen I,” 1889, p. 203. In 
one specimen at the Cambridge Botanic Garden, however, six of the tubers 
had produced stolons at their distal ends. 
Attention may incidentally be drawn to the appearance of chlorophyll in 
the superficial layers of the young tubers as well as in some young under¬ 
ground stolons, before these organs have been exposed to light. 
4 Attention may here be drawn to a minor point, namely, that whereas in 
the aerial stolon there are usually four very well marked protoxylem strands, 
in the underground stolons they are neither constant in number nor so well 
differentiated and regularly distributed. 
