62 LINNEAN SOCIETY OK LONDON. 



there is frequently an atropliied uucleuH w lien the smaller mini hers 

 are t'ormed. The division ot" the conjugation miclens into four, 

 and the accimudation of the cytoplasm etc. into four Desmid 

 mother-cells, each with a distinct nucleus, is abundantly shown by 

 my microscope preparations. There are a great many zygospores 

 wliie-h show this most clearly. It is to be seen in the spores 

 whilst they are still associated Avith the old semi-cells of the 

 parent Desmids. The protoplasmic masses at tliis stage are con- 

 nected by threads only, and are divided by broad spaces; they 

 appear to increase in size in the older zygospores, many of which 

 show the component parts of the tetrad consisting of naked masses 

 of ])rotoplasni, only separated by the merest line — they are prac- 

 tically in contact, except at the point where three mother-cells 

 ap]n'oxiniate. I was some time before 1 found the division of the 

 cell-contents into two parts; this phase is much less abundant 

 than the tetrad one. 



When 1 Knd the young Desmids enclosed in the protoplasm, 

 I have no hesitation in saying that they have been formed from the 

 spore. There are many amoeboid masses of protoplasm on the slides 

 wliie-h do not show this, and they may, or may not, constitute the 

 early stage of the escaped contents. The first indication of the 

 production of the young Desmids is the formation of a hyaline 

 district surrounding a central area, nuclear mass, or masses. These 

 soon show the outlines of the Uesmids. I lind two almost mature 

 in each moss most commonly : there are few slides out of the 

 several dozen which I have prepared which do not contain at 

 least one specimen showing this ; many have three or four. The 

 number showing one Desmid only is approximately the same ; 

 the majority are of the tri-radiate form, one or two show the 

 tetra-i'adiate modification only. The number of clusters of three 

 embryonic Desmids is less than that of the little clusters of 

 two, and I have seen perhaps half-a-dozen clusters of four — the 

 four nuclei do not always survive. I have found four dead, also 

 eight empty semi-cells, enclosed in a surrounding membrane — the 

 remains of the enclosing protoplasm. 



The protoplasm surrounding the young Desmids is very granular 

 at first, and I have three or four times seen the same protoplasmic 

 mass containing three-rayed and four-rayed forms. One of the 

 best examples of this escaped capture, one has moved, but I still 

 have one or two slides illustrating this phenomenon. 



The vegetative division of the Desmid is sometimes of the 

 normal type, namely that a bulging protuberance is formed by 

 each semi-cell, the two swellings being soon covered by a cell- 

 wall and gradually increasing in size till they reach the dimensions 

 of the old semi-cell. In other instances only one circular central 

 cell is formed between the semi-cells ; this sometimes elongates 

 wnth the production of an hour-glass contraction in the centre, 

 and two Desmids result. In a third method a central heart- 

 shai)ed cell is formed by the asymmetric divison of the bulging 

 portion ; the two terminal semi-cells approach each other, the 



