OF THE DESMIDIE^. 17 



thinner, as if giving way at that spot. On the third morning the membrane 

 had broken and the granules escaped, leaving the nearly emptied case" 

 (I. 12). 



Inasmuch as a sporangium may pass successively from a smooth to a spinous 

 condition, it follows that the transitional stages of one species may be mistaken 

 for the final stage of another ; hence a difiiculty in determining to what plant 

 detached scattered sporangia may belong. It is only, indeed, when these seed- 

 capsules occur in company with the fronds producing them that we are enabled 

 to pronounce decisively by what species they are generated. 



As the foregoing account of conjugation and sporangia passed through the 

 press, we met Tvdth the valuable paper of Dr. Hofmeister on the propagation 

 of the Desmidieee and Diatomeae, translated by Prof. Henfrey from the 

 Report of the Natural History Society of Saxony for 1857. This commu- 

 nication tends to clear up the questions of the nature of the sporangia and of 

 the relation of theii' contents to the propagative process. The conciseness of 

 the description renders abridgment undesirable ; and we accordingly present 

 it (so far as it relates to the points in question) as it stands in the Annals of 

 Natural History (1858, i. p. 2) :— 



" The conjugated indi\iduals of Cosmariwn tetraojjhthahmm displayed 

 exactly the behavioui* which Kalfs has represented and Braim described of 

 those of Cosmarium margaritiferum. The Cosmrtr/a which had commenced 

 the conjugation process appeared cracked apart at the constricted place in the 

 middle. Into each of the halves of the tuberculated cell- coat of the two 

 mother-indi\'iduals extended a continuation of the membrane of the conju- 

 gation-ceU. This smooth membrane completely lined the interior of the 

 tuberculated half-shells. The contents of the conjugation -cell revealed no 

 definite arrangement ; they were mostly accumulated in the middle into an 

 irregularly-shaped ball ; in other cases separated into several such balls, part 

 of which extended even into the split haK-sheUs of the mother-cell. With 

 these conjugated individuals, in the same fiuid, occuiTed (very sparingly) par- 

 ticular specimens which bore, in the middle space between the two separated 

 half- shells, a broad, delicate- walled utricle, the circumference of which about 

 equalled that of the two half-ceUs taken together. The arrangement of the 

 cell- contents in the primary portions of the cell did not appear essentially 

 altered ; the contents of the intermediate expansion consisted of a thick coat 

 upon the wall of granular protoplasm "svith sparingly-scattered chlorophyll. 

 This condition is probably that which immediately precedes conjugation, 

 originating by excretion of new cellulose at the deepest part of the constric- 

 tion, after the cracking of the membrane and separation of the primary halves 

 of the cell, exactly as in normal cell- division, from which this process can 

 only be distinguished by the omission of the formation of a septum at the 

 narrowest part of the isthmus. Similar phenomena have been observed by 

 Niigeli in Cosmarium crenulatum, and by Mrs. Herbert Thomas in Cosmarium 

 margaritiferum (scarcely specifically distinct from C. tetraophthalmimi), only 

 that here the intermediate piece of the Alga did not conjugate with the 

 similar piece of another individual, but, producing tubercles on its outer 

 surface, continued the vegetative life. 



" In other conjugation-cells there lay, in the middle part of the conjugation- 

 cell, a globular ceU enveloped in a rather thick membrane, of gelatinous 

 aspect, and smooth on the outside (the spore). No intermediate stages could 

 be found between this and the previously- described condition. Experiments, 

 in which an attempt was made to obtain a completion of- the less-advanced 

 conjugation under the microscope, all failed. Apparently the conjugation- 

 ceU is exceedingly sensitive to any external injury, especially to contact with 



