14 W. Hofmeister on the Propagation 



cellulose projecting inward from the internal wall, intersecting 

 at an angle of 60° ; these ridges grow in toward the middle 

 point of the cell, like the annular ridge of Cladophora at the com- 

 mencement of cell-division. When these projecting ridges have 

 attained the breadth of a fourth part of the transverse diameter 

 of the mother-cell, the cell-contents divide into four parts, which, 

 retracting from one another and from those ridges, occupy the 

 four chambers of the cell, each of which is vaulted externally 

 and bounded laterally by three of the ridges, — here becoming 

 coated with a membrane and developed into a spore, while the 

 tetrahedral space in the middle of the cell, bounded by the six 

 ridges, remains filled only with watery fluid*. The spores be- 

 come free by the solution of the enveloping part of the mem- 

 brane of the mother-cell. The resemblance of this process to 

 the vegetative multiplication of Navicula consists in the inter- 

 ruption of the division of the cell by the formation of septa, and 

 the subsequent completion of the daughter-cells by secretion of 

 membrane on the external surface of contracted portions of the 

 contents of the mother-cell. A deviation occurs in the circum- 

 stance that in Pellia the segment of the coat of the mother-cell 

 which is in contact with the external surface of the daughter- 

 cell becomes dissolved, while in Navicula it persists and remains 

 most intimately connected with the daughter-cell. 



The newly-formed parts of the cell-coat facing together in the 

 division, ai'e in the Diatomefe, and still more clearly in the Desmi- 

 diese, perfectly smooth and even for some time after their pro- 

 duction ; it is subsequently that they obtain the often very con- 

 siderable tubercles and spines, consisting principally of cellulose. 

 The same applies to the processes upon the outer integument of 

 the spores of Euastra, Cosmaria and Staurasti'a produced in the 

 conjugation. These phsenomena, as also the autumnal secretion 

 of jelly by many of the Desmidiese, deserve more notice than 

 they have hitherto attracted in connexion with the theory of the 

 life of the vegetable cell. Still more remarkable behaviour is 

 displayed by the cell-coat of an organism which 1 refer only 

 doubtfully to the Desmidieae. In many pools about Leipsic, in 

 which Desmidiese abounded, occurred large, accurately spherical, 

 thick- walled cells, some as much as "05 millim. in diameter, 

 rich in chlorophyll, which not only lined the internal wall as a 

 connected granular layer, but — as in many Desmidieaj — formed 

 groups, distributed, in the interior of the cell, in a system of 

 radially arranged plates, which presented a stellate appearance 



* Hofmeister, Vergleich. Untersuch. p. 20. [This is apparently com- 

 mon in the spore-formation of Hepaticae : we have observed it in Mar- 

 chantia. — A. H.] 



