There is an unbroken series of intergrades between a leaf and an air vesicle in H. dioica. The origin of air chambers seems to be a matter of food relationships in which hyphae play an important part. The fucosan of Hansteen seems to be a fucoxanthin plastid. Protoplasmic connections are continuous throughout the plant. The early development of the conceptacle stresses the upper rather than the basal cell, as preceding work on the European species had shown. The frequent appearance of double conceptacles may be due to the action of 2 initials upon a single intervening wall cell.