10 
SIPHONACEiE. 
these genera the component filaments remain in the ordinary state of cellular tissue, 
having their membranous walls composed of cellulose, and filled with endochrome. The 
only further change which the plants of this group exhibit in structure consists in a 
secretion of carbonate of lime, which in several genera is found coating the external 
surface of the cells ; and sometimes, as in Halimeda and some species of XJdotea , 
surrounding the cells in such abundance as to cover the whole frond with a smooth 
coat of plaister, and obliterate all appearance of filaments. In such cases it is necessary, 
in order to see the structure, to macerate a portion of the frond in hydrochloric acid, 
until the lime be removed. When so treated, the component cells may be extracted 
and will be found to be of similar nature to those of Codium or Bryopsis. Indeed 
through some species, such as TJdotea membranacea , there is an almost direct passage 
into Codium. 
A more compound structure exists, as will be afterwards more fully described, in the 
sub-order Caulerpece , where from the inner face of the cell-wall innumerable branching 
and anastomosing processes issue, and fill up the cavity of the cell with a spongy, 
filamentous substance, unlike any structure noticed within the cavity of any other 
vegetable cells ; so far as I am aware. On this remarkable character several authors 
propose to separate these plants into a distinct Order, and to this proceeding my only 
objection is that it appears to be an unnecessary multiplication of Orders. 
The fructification of these Algge has been observed in several but not in all, and 
presents some modifications in the different genera. In some, as in Bryopsis , the whole 
substance of the endochrome in fruiting specimens is changed into minute zoospores , 
which when emitted from the parent have an apparent voluntary movement like that 
of infusoria ; swimming backwards and forwards by means of retractile cilia, which only 
disappear when the zoospore finds a point of fixture, and commences to germinate. In 
others, as in Codium , similar zoospores are developed within special encysted fruit-cells 
or vesicles, called by Agardh coniocystce , which arise from the branches and are divided 
by a diaphragm from the branch on which they are formed. In others, as in Vaucheria , 
zoospores of a higher development are formed within similar cysts ; and in this genus 
the cyst (or ovary) is accompanied by a well formed antheridium. 
The process of fertilization of the spore in Vaucheria has recently been ably investi- 
gated by Pringsheim, a French translation of whose memoir on the subject will be found 
in Ann. Sc. Nat. Ser. IY. vol. 3, p. 363. The existence of two organs in Vaucheria, 
one of which was supposed to be an antheridium, had been noticed originally by Vaucher 
half a century ago, and they have passed under the eyes of succeeding observers ; but 
no one appears to have actually watched the process of fertilization until it was 
discovered and published by Pringsheim in 1855. I shall merely give an abstract of 
the process, referring for full particulars, illustrated by beautifully executed figures, to 
the above quoted memoir. The anther or corniculum in Vaucheria consists of a small, 
cylindrical spirally curved or helicoid process rising from one of the branches of the 
frond, and at first not differing from an ordinary branchlet except in size. But 
gradually a change takes place in its contents, at first manifested by a loss of colour in 
the matter filling the upper portion of the young antheridium. Then a diaphragm is 
formed, which walls off the portion toward the extremity of the antheridium from the 
