EUPHYCOPHYTA 24I 



are jointed, cylindrical or compressed, arise from calcified en- 

 crusting basal discs or prostrate interlaced filaments. Branching, 

 which is frequent, is pinnate, but in the closely allied genus Jania 

 it is dichotomous. There is a central core of dichotomously 

 branched filaments with oblique filaments growing out at the 

 swollen internodes to form a cortical layer, the end cells being 

 flattened, the whole being encrusted by lime except at the joints. 

 The plants are monoecious or dioecious, the reproductive organs 

 being borne in terminal or lateral conceptacles. The carpo- 

 gonia, which are not calcified, arise from a kind of prismatic disc 

 formed from the terminal cells, these cells also functioning later as 

 the auxiliary cells. As a result of oblique divisions, one to three 

 embryo carpogonial branches are formed on each mother cell, but 

 only one of these finally develops into the mature two-celled carpo- 

 gonial branch with its long trichogyne. After fertilization a long or 

 rounded fusion cell is formed by the auxiliary cells, and this con- 

 tains both fertilized and unfertilized carpogonial nuclei. The 

 antheridia are much elongated, and after hberation the spermatia 

 round off and remain attached to the antheridial wall by means of a 

 long, thin pedicel in C. officinalis and by a short stalk in Jania 

 rubens. The tetrasporangia comprise a stalk cell and sporangium in 

 which the four spores are arranged in a linear row as in Epilithon. 



Cuq-reocolacaceae: Harvey ella (after W. H. G. Harvey). Fig. 135 



This and the closely allied genus Holmsella are monotypic genera 

 each containing a holo-parasitic species, whilst Choreocolax is an- 

 other parasitic genus very nearly related to them. Harvey ella 

 mirahilis is parasitic on species of Rhodomela whilst Holmsella 

 pachyderma parasitises Gracilaria confervoides. They have littie or 

 no colour of their own as might be suspected from their parasitic 

 nature, and they send out branched filaments or haustoria into the 

 tissues of the host. The haustoria penetrate the middle lamellae of 

 the host cells and form secondary pit connexions with them. The 

 parasites appear as external cushions lying on the branches of the 

 host, each cushion, which is surrounded by an outer gelatinous 

 coat, consisting of a central area that is four to five cells thick. In 

 Harveyella the female cushions bear numerous procarps with four- 

 celled carpogonial branches each with two sterile branches. In 

 Holmsella the carpogonial branch is two-celled. The antheridial, 

 carpogonial and tetrasporic plants are all separate, and the species 



