86 
G. P. DARN ELL-SMITH ON 
chromoplasts) often slightly raised from the surface become noticeable (fig. 4). At 
this period the nucleus of the spore has divided into two ; of the daughter nuclei 
one remains within the spore and one travels towards the brownish area at the top 
of the protuberance. The droplets in the spore become more transparent, and many 
of them pass out into the growing portion. The area containing the chromoplasts 
is same what bulged, and, the cell membrane being delicate, it is very liable to 
become slightly invaginated at this point, a false fold thus apparently cutting off 
the yellowish cap that is destined later to become the apical cell (figs. 6 and 7). 
3. Developmental Stages. 
Later a transverse wall appears, cutting the cell in two in a plane at right angles 
to the axis of emergence. There is thus formed a basilar cell and an upper cell. 
The extine of the spore clings as a mere shell to the basilar cell, which is large and 
globular ; in this position it may remain some time. In the upper cell two series of 
segments arise by inclined walls formed alternately right and left. Growth at first 
is slow ; from the first emergence from- the spore to the three-celled stage takes 
three weeks. By the time the third cell wall has formed, the colouring matter of the 
chromoplasts of the now constituted apical cell becomes more diffuse and the chromo- 
plasts begin to lose their distinctness. Little papillae may be found here and there 
upon the large apical cell (figs. 5 and 8). A further division of cells gives rise to a 
small cell -mass, which is early penetrated by an endophytic fungus. The first fungus 
threads I have seen have been at the three-celled stage. The cells of the first cell- 
mass are very light brown in colour, and become heavily infected with fungus. 
Usually there is a fairly well-marked point at which the interrelationship of fungus 
and host seems to be well established ; from this point onwards nearly all the cells of 
the prothallium except the external layer are almost full of dense skeins of fungal 
hyphae, and are darker in colour than the earlier-formed cells. The prothallium 
widens rapidly till it attains the diameter that it will approximately retain through- 
out its growth (fig. 19). 
Note. 
Before passing to a consideration of the mature prothallus, which hears both male and female organs, 
it will he convenient to refer here to a communication made by Mr T. Whitelegge to the Linnean 
Society of New South Wales on April 26, which I give in full, and with which I find myself in entire 
disagreement : — 
“ Mr T. Whitelegge exhibited a series of mounted slides illustrating the sexual generation of Psilotum 
triquetrum. The spores were grown on the living rhizomes of Davallia pyxidata, in a small Wardian case. 
The spores of Psilotum , although isosporous, are strictly dioecious. The male gametophyte consists of about 
eight cells. These are unequal in size, with clear, thin walls, enclosing very many extremely minute 
antherozoids. The cells are distinct, being only slightly adherent to each other, easily detached, and often 
float free when placed in water. The larger cells are equal to the diameter of the spore, the smaller to that 
of the nucleus. Spores destined to produce the female gametophyte contain an indefinite number of small 
cells. A single dome-shaped body emerges from the centre of the spore, and is about equal to its diameter. 
The structure consists of many irregular cells, apparently held together by gum ; some project on the sides 
