184 Alternation of Generations in the Dictyotacece. 
arrangement of groups of sclerenchyma in association with the 
vascular bundles in the leaf (sometimes of more than specific value), 
the structure and relative magnitude of palisade and spongy 
parenchyma (a very uncertain character in most cases), the degree 
of development and marking of the cuticle, the disti ibution of the 
stomata, the size and shape of the epidermal cells in surface \ie\\ 
and the protrusion of epidermal cells into papillae; owing to the 
easy determination of this last feature it is often an excellent specific 
character. The presence of hypoderm and its structure, as well as 
the transcurrency or embedded character of the vasculai bundles in 
the veins of the leaf vascular bundles of the veins either con¬ 
nected with both epidermes by means of strands of collenchyma or 
sclerenchyma, or embedded in the parenchyma of the leaf) are 
characters which are not rarely constant for larger groups of 
affinity. 
From the phylogenetic point of view the structure of the 
seedlings is most important, as has been sufficiently shown by Miss 
Sargant’s recent work on the Monocotyledons. In the seedling we 
may expect to find a very uniform type of structure throughout large 
groups and an examination cf the same may in many cases make it 
possible to determine those characters of the adult plants which 
are due to their ancestral tendencies. At the same time the 
anatomy of the seedling may be expected to indicate affinities more 
clearly than that of any other part of the plant. 
University College, London, F. E. Fkitsch. 
July, 1903. 
ALTERNATION OF GENERATIONS 
IN THE DICTYOTACECE, 
(Abstract of a Paper read before Section K of tlie British Association 
at Southport). 
I N the Dictyotaceae the asexual cells are always borne on 
distinct plants from those that produce the sexual cells. The 
antheridia and oogonia may appear together on the same plants as 
in Padiua, or on separate individuals as in Dictyota, but the 
tetrasporangia are never found on the same plants as the sexual 
cells. In view of this fact it is an interesting question whether the 
tetrasporic and gamete-bearing plants represent the sporophyte 
and gametophyte generations respectively, and whether they 
