174 BOTANICAL GAZETTE. 



be replaced by a layer of cellulose, which presents spiral striatioa 

 corresponding to the previously existing rows of microsoniata, 

 and which constitutes a thickening layer of the cell-wall. In cells 

 the walls of which become much thickened, the whole of the 

 protoplasm may be gradually used up in this way. Again, the 

 wall of pollen-grains and of spores is formed from a peripheral 

 layer of the protoplasm which contains abundant microsomata. 

 Its subsequent growth, and especially the development of the as- 

 peritus which it commonly presents, is effected by the surrounding 

 protoplasm which is derived from disorganized tapetal cells ; this 

 is especially well shown in the development of the epispore of 

 Equisetum and of Marsilia. When an intine or endospore is pre- 

 sent it is produced like the outer coat from a peripheral layer of 

 the protoplasm of the pollen-grain or spore. Further, the septum 

 which is formed in the division of a cell is produced in the same 

 way. 



The cell plate, like the peripheral layer of the protoplasm of a 

 young pollen grain, contains microsomata which disappear, and it 

 is then converted into a plate of cellulose. Finally, the successive 

 layers of a starch grain pre produced by the alteration into starch 

 of layers of proteid-substance derived from the starch-forming cor- 

 puscle (amyloplast). 



Professor Strasburger next points out that the starch which 

 makes its appearance in the chlorophyll-corpuscles under the influ- 

 ence of light, is derived from the proteid of the corpuscles by dis- 

 sociation. The formation of this starch is therefore not the imme- 

 diate product of the synthetic processes going on in the chloro- 

 phyll-corpuscles, but only a secondary product. The processes in 

 question produce proteid. Prof. Strasburger is inclined to accept 

 Erlen Meyer's hypothesis that methyl aldehyde is formed in the 

 chlorophyll-corpuscles from carbon dioxide and water, and to be- 

 lieve that by polymerization a substance is produced which can 

 combine with the nitrogenous residues of previous dissociations of 

 proteid to reconstruct proteid. He does not agree with the sug- 

 gestion of Loew and Bokorny that the methyl aldehyde may con- 

 bine with ammonia and sulphur to form proteid de novo. 



Lastly, Prof. Strasburger makes a suggestion as to the probable 

 physiological significance of the nucleus. He points out that the 

 nucleus cannot be regarded as regulating cell-divisions ; for in- 

 stances are known of cell-division taking place without previous 

 nuclear divisions, and conversely, of nuclear-division taking place 

 without cell-division. He is of opinion that the nucleus plays an im- 

 portant part in the formation of proteid in the cell. This view is 

 founded upon the fact that one or more nuclei have been found to be 

 present in the vast majority of plant-cells, that the nucleus is, as a 

 general rule, the most persistent protoplasmic structure, and that it 

 gives the various proteid reactions in a very marked manner. 



