276 W. H. GILBURT ON ABSENCE OF STOMATA IN CERTAIN FERNS. 



always midway between the veins, the greater number being those 

 immediately surrounding them. 



In Todea we have again another variety of structure, there being 

 one layer of cells at the margin, increasing to two immediately, and 

 then to three as we get farther towards the veins. The intermediate 

 layers of cells are much larger, and are roughly hexagonal in out- 

 line, when the frond is viewed by transmitted light. 



The superior and inferior layers of cells in both Todea and 

 Trichomanes membranaceum are very largely supplied with 

 chlorophyll, while the intermediate layer contains little, if any ; 

 showing that, at least far the largest share of work, in the elabora- 

 tion of the crude sap of the plant is performed by these exterior 

 thin-walled cells. 



There is one feature worth noticing in Todea pellucida, i.e., in 

 those parts where the three layers of cells exist, the superior and 

 inferior ones take on the irregular wavy outline of the ordinary 

 cuticle cell, though having no other character in common. Here it 

 would appear that we have indications of an approach to the more 

 highly developed and differentiated fronds of other ferns. 



In the stipes of these species there is also a variation from what 

 we generally find in the same parts of other ferns. Commencing 

 from the outside we find a single layer of chlorophyll-containing 

 thin-walled cells. Next in order we have a layer of close-fitting, 

 greatly elongated cells, very small in diameter, and with walls 

 much thickened, but apparently without markings. These cells, as 

 we work towards the middle of the sections, gradually increase in 

 diameter, and decrease in thickness and length, till we come to the 

 woody bundle which occupies the centre. 



All the cells are cylindrical in form, the ends being usually set 

 together at nearly right angles to their greatest length, and all 

 except the outer layer, at this time of year, are filled with starch, 

 and in none but the outer thin-walled layer have I found a trace of 

 chlorophyll. This arrangement holds good as the stipes passes into 

 the midrib and throughout its ramifications. 



Thus from a consideration of the structure of these Ferns we may 

 fairly conclude ; there is no place for stomata in their tissues, and no 

 purpose they could serve in the economy of the plant. 



Note. — Since reading the above, my attention has been called to a mono- 

 graph on the Hymenophyllacem, published at Prague in 1843, by Prof. Dr. 

 Karl B. Pn sf , in which he refers to the absence of stomata in this genus. 



in the case of Todea, however, I have not been able up to the present 

 time to find any note of their absence having been before observed. 



