1G2 CASPARY, ON THE ZOOSPORES OF CHROOLEPUS. 



contents ; and therefore in Chroolepus aureum, where the cell- 

 contents are rendered brown by iodine, he cannot say whether 

 the whole of the covering, or only its apex, is unaffected by 

 the iodine. But inasmuch as, in C. umbrinum, the zoospore, 

 even after treatment with a strong solution of iodine and 

 iodide of potassium, exhibits, on account of its amylaceous 

 nature, only a dirty blue colour, and not a brown, it seems 

 probable that the whole remaining portion of the cell-cover- 

 ing is of the same nature as its apex, that it is not coloured 

 brown, and consequently is not nitrogenous. From its 

 behaviour under iodine and sulphuric acid, the cell-covering 

 probably does not consist of cellulose, although in the present 

 state of microscopical chemistry it is not easy to say accurately 

 of what it does consist. The observation, however, is an 

 interesting addition to our knowledge of the nature of the 

 covering of zoospores, which covering has hitherto been sup- 

 posed to be always coloured brown by iodine, and to be there- 

 fore nitrogenous. At all events the cell-covering, or at least 

 the apical portion, cannot in Chroolepus be looked upon as a 

 primordial utricle. It Mould seem that the subsequently 

 formed cellulose membrane of the cells of Chroolepus is pre- 

 sent in the zoospores at the period of swarming, but that in 

 this condition the young membrane does not exhibit the con- 

 sistency or the reactions which are afterwards visible in it. 

 The author then proceeds to observe, that the existence of so 

 peculiar a membrane is less surprising, as there are several 

 other algse which exhibit unusual chemical peculiarities in 

 their cell- coverings; and after noticing several instances of 

 such algae, he concludes that there are modifications of 

 cellulose dependent upon the age and the species of the plant, 

 which do not exhibit the usual reactions ; and that it is there- 

 fore fair to assume that the membrane of the zoospores of 

 Chroolepus, or at least the colourless apex of the membrane, 

 consists, at the period of swarming, of a modification of 

 cellulose not exhibiting the usual reactions, whilst the zoo- 

 spores of otber plants are only clothed with a nitrogenous 

 primordial utricle. 



The young membrane of the zoospores of C. umbrinum is 

 very delicate, and disappears soon after the death of the 

 zoospores, of which a few only lived to vegetate. The brown 

 granular contents of those which died escaped in all directions 

 (exhibiting active molecular motion) very shortly after the 

 cessation of the motion of the zoospores, showing that the 

 cell-wall did not burst, but dissolved. (Sec fig. £4.) Fig. 23 

 shows the remnants of a zoospore, consisting of a heap of 

 granules surrounded by a gelatinous mass (*) which belonged 

 to the cell-contents, not to the membrane. Iodine did not 



