27 2 Hill . — ( 9 /z //?<? Presence of a Parichnos in Recent Plants . 
them also to supply the place of the lenticels of the recent dicotyledonous 
trees.’ 
As regards the parichnos of recent plants, I believe that it is primarily 
concerned in the production of mucilage, which would be of value to the 
reproductive organs in preventing their desiccation in times of comparative 
drought. And it is primarily for this reason that the structure has 
persisted. 
The fact that the parichnos is chiefly restricted to the sporophylls of 
recent plants, as far as has been seen, bears out this opinion. If this view 
be accepted, it would explain why, in a plant like Isoetes lacustris> the 
parichnos does not occur ; for, of course, its presence would be quite 
unnecessary in a plant which leads a submerged aquatic existence. 
It does not follow, however, that this was the function in the 
plants of past ages. In some cases this role may have been performed, 
more especially where the parichnos occurred in the strobili. But, on the 
other hand, it may not hold in those cases where the tissue occurs in the 
vegetative leaves. In some instances, the appearance of the parichnos does 
warrant the assumption that it was of a secretory nature ; contrariwise the 
facts relating to their persistence, enlargement, and lenticel-like nature in 
many cases favour the views held by Scott and Weiss. It may be 
remarked that this latter opinion is not necessarily antagonistic to the 
former, for it is possible that a secretory function was first performed, and, 
when the leaves had been shed, was followed by a respiratory role. 
It may be remarked that if any phylogenetic value be assigned to the 
parichnos, then its presence in Isoetes gives additional support to the view 
that this plant belongs to the Lycopodineae. The writer is of the opinion 
that the parichnos has a phylogenetic value. 
In conclusion, I desire to express my thanks to Dr. D. H. Scott, F.R.S., 
Professor F. W. Oliver, F.R.S., Mr. E. C. Jones, F.L.S., and the Authorities 
of the Royal Gardens, Kew, for their kindness in supplying material. 
It should also be mentioned that this research was commenced in the 
Jodrell Laboratory, Kew, and finished in the Medical School of St. Thomas’s 
Hospital. 
