2 16 Possible Existence of a Lattice-Work Fern Stem. 
stem was still preserved in excellent condition ; and here it was 
easily ascertained that the very early leaves of the young plant had 
no epidermal pockets in their axils. Again when at length these do 
appear they are at first comparatively shallow, and end blindly in 
the cortex without reaching so far in as the vascular ring. 
The similarity between the development of these remarkable 
fern stems, and the manner in which their particular type of 
vascular system is assumed to have arisen, is very striking; so much 
so that the temptation to carry the analogy a step farther, and to 
speculate upon the possible existence of a stem possessing a struc¬ 
ture corresponding to the tubular condition of the stele, is almost 
irresistible. It is only wanted that the epidermal pocket from each 
leaf should become continuous with those from the leaves inserted 
lower down, and the stem itself would become a lattice-work tube. 
In Onoclea germanica they sometimes very nearly do so, but actual 
continuity was never seen to occur. Moreover, it is very difficult to 
imagine how such a stem could possibly arise from an apical meri- 
stem with a single initial cell ; except, perhaps, by some such clumsy 
expedient as the supposition of a one-sided growth that would shift 
the initial cell all round the termination of the tube. But I know of 
no precedent elsewhere for such a mode of growth. These fern stems 
present, of course, no difficulties to those who regard the sporophyte 
stem as a system of concrescent “ phytons,” or “ shoot-segments,” 
which arise successively one upon another. According to this 
theory the free terminal part of the “ shoot-segment ” becomes the 
leaf, while the basal part fuses with the bases of other “ shoot- 
segments” to form the aggregate stem. If, with Celakovsky, each 
“ shoot-segment” be regarded as an individual, and equivalent to a 
Bryophyte sporogonium, the whole plant now becomes a composite 
organism consisting of repetitions of a sporophyte by some form of 
budding, each individual with its own independent growth. It 
appears to me, however, that the theory of “phytons” receives no 
real support whatever from the plants in question, for their type of 
stem structure cannot in any sense be regarded as primitive. It is, 
on the contrary, in each particular case, the latest expression of a 
long series of advances from the primitive solid stem, with its 
single solid central protostele. 
