10 SIPHONACE.E. 



these genera the component filaments remain in the ordinary state of cellular tissue, 

 having their membranous walls composed of cellulose, and filled with eudochrome. 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 HaUmeda and some species of Udotea, 

 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 Udotea membranacea, there is an almost direct passage 

 into Codium. 



A more compound structure exists, as will be afterwards more fidly described, in the 

 sub-order Caulerjme, where from the inner fixce 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 Alg£B has been observed in several but not in all, and 

 presents some modifications in the difitrent genera. In some, as in Bryopsis, the whole 

 substance of the endochrome in fruiting specimens is changed into minute zoosp>ores, 

 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 coniocyshe, which arise from the branches and are divided 

 by a diaphragm from the branch on which they are formed. In others, as in Vaiicheria, 

 zoospores of a higher development are formed within similar cysts ; aud in this genus 

 the cyst (or ovary) is accompanied by a well formed anther idium. 



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. IV. 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 beautifidly 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 difiering 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 



