Bryopsidaceas 225 



connection with the zoogonidangia. The branches, which are from 10 to 15 /A in diameter, 

 ramify through the tissues of the leaf, traversing both cells and intercellular spaces. 

 Near the epidermis of the leaf the branches become swollen in a moniliform manner, 

 attaining a diameter of 30 /A or more, and those which are in the epidermis often develop 

 elongated tubular hairs (4 5 /x in diameter), devoid of any colour, which stand out more 

 or less at right angles to the surface of the leaf. There is a parietal layer of protoplasm 

 enclosing a central vacuole which is only interrupted at the constrictions of the coanocyte. 

 The chloroplasts are very numerous and discoidal, with polygonal outlines, and each one 

 contains a small central pyrenoid. The nuclei are fairly numerous and large, each with a 

 conspicuous nucleolus ; they occur at scattered intervals in the lining layer of protoplasm 

 and are always internal to the chloroplasts. 



The zoogonidaugia are separated from the rest of the ccenocyte by a wall, after which 

 the nuclei divide and the disc-like chloroplasts become orientated at right-angles to the 

 wall, Numerous zoogonidia (12 15 /* in length) are formed, which are at first clustered 

 as a botryoidal mass, but they soon develop two cilia and finally escape through the 

 tubular hairs. Each zoogonidium possesses several chloroplasts and a conspicuous 

 pigment spot. 



Huber's suggestion that Cheetosiphon may be the extreme form of a chtetophoraceous 

 series passing through Endoderma, Phseophila and Blastophysa does not appear to be at 

 all probable. From its siphonaceous thallus and the nature of its chloroplasts it is. far 

 more likely to be a member of the Siphonales allied to the Bryopsidaceas, its special 

 peculiarities being due to its endophytic habit. 



Family Bryopsidaceae. 



In this family the thallus is a much branched coenocyte, the lower 

 branches becoming modified as root-like organs of attachment. The upper 

 branches are arranged as shoots, each with a main ascending axis or ' stem ' 

 and branches of the first and second order which are often described as 

 ' leaves.' The whole plant consists of graceful feather-like fronds of a deep 

 green colour which have a superficial resemblance to certain species of 

 Caulerpa. The 'leaves' are of a fusiform-cylindrical shape, having a marked 

 constriction at their point of junction with the axis, and are arranged either 

 in two rows or in a spiral. When they become fully mature in Bryopsis 

 they are cut off from the axis by a wall and converted into gametangia 

 (fig. 146 ./). The latter eventually fall off leaving the separating walls as 

 scars along the axis. In Pseudobryopsis the ' leaves ' are from the first cut 

 off by a transverse wall from the axis. 



The cell-wall is thin and not encrusted. Wille ('97) stated that trabeculae 

 sometimes occur, such as those present in the coenocytes of Caulerpa, but 

 this observation is apparently doubtful. The protoplasm forms a parietal 

 layer in which there are numerous nuclei and chloroplasts. The latter are 

 small elliptic discs with a central pyrenoid. In the large cell-sap vacuole 

 which occupies all the central space of the coenocyte there are rounded and 

 spindle-shaped albuminous bodies, first observed by Noll. 



w. A. 1 5 



