188 Anatomy of Acrostichum auretirti. 
It is frequently contended that a moister climate obtained 
during the carboniferous epoch, and however this may be with 
regard to general atmospheric conditions, 1 it is clear that a damp 
heavy air would exist in the swamp itself. 
If future knowledge should prove that such really were the 
conditions under which the greater number of the ancient Lycop- 
sids flourished, and evidence accumulate in favour of the view that 
such plants were essentially ill-adapted to the driest terrestrial con¬ 
ditions, 2 we should be furnished with a clue to the cause of the 
decadence of this group and the total extinction of its arborescent 
forms. 
It has been pointed out to me that mountain ranges are the 
best means of wide distribution, and from such situations these 
plants would, on our hypothesis, necessarily tend to be excluded. 
The lines of thought suggested by the examination of Acrosti¬ 
chum aureum have led me rather far into the realms of pure 
speculation, and for this I must beg to be excused. 
My warmest thanks are due to Professor Oliver and to Mr. 
Tansley for their very kind and helpful interest in the progress of 
the work. 
1 Seward, “Fossil Plants as Tests of Climate.”—Sedgwick Prize 
Essay, 1S92. 
2 Monarch roots must be less effective as absorbent organs than those 
furnished with more than one protoxylem group. 
EXPLANATION OF PLATES. 
Plate III. —The Root. 
Fig. 1. Portion of middle lacunar cortex of root as seen in transverse section 
(Fig. 3) enlarged. The vertical arms of its irregular cells seen on end—most 
show a pitted area, (x 100). 
Fig. 2. Single cell of tissue shown in Fig. 1 under greater magnification, p.a., 
pitted area, (x 400). 
Fig. 3. Tranverse section of stout root. o.c., outer cortex ; m.c., middle 
lacunar cortex; i.c., inner sclerenchymatous cortex; end. and per., endo- 
dermis and pericycle; d.px., double protoxylem group of stele; s.px. 
single protoxylem group, (x 17). 
Fig. 4. Single cell of tissue shown in Fig. 1. p.a., pitted area (cf. Fig. 2). 
(x 400). 
Fig. 5. Portions of three cells of tangential wall of lacunar chamber of middle 
cortex as seen in tangential longitudinal section (cf. Fig. 6). p.a., lateral 
view of pitted area between arms of neighbouring cells. ( x 400). 
Fig. 6. Portion of middle lacunar cortex of root as seen in tangential longi¬ 
tudinal section, rad. w., cells of radial walls of lacunar chambers seen 
on end, many show pitted areas; tan. w., cells of tangential wall viewed 
fiom the side, (x 100). 
