October 15, 1891] 



NATURE 



581 



cided advance on Schleiden's theory of free-cell formation, for 

 Nageli maintains that the special mother-cells are not formal 

 directly around a cytoblast (nucleus) but around the whole 

 granular contents, in the middle of which a free cytoblast lies. 

 It was long, however, before Nageli completely freed himself 

 from the influence of Schleiden's histological theories. It is 

 interesting that in this paper he described ani clearly figured 

 the two nuclei in the pollen-grain of an OEnothera, th mgh he 

 did not know that this was a constant phenomenon. The im- 

 portance of this observation was not appreciated until Eifving, 

 Strasburger, and Guignard, investigated the subject in our 

 own day. 



Nageli's " Botanische Beitrage " contributed to the volume of 

 Linncca for 1842, include some important papers. In those on 

 the development of stomata and on cell-formation in the root- 

 apex, he endeavoured to reconcile his own accurate observations 

 with Schleidenian theories, and was thus led to oppose Unger, 

 who had already recognized that vegetative cell-formatinn is a 

 process of division. A paper on Fungi in the interior of cells is 

 interesting, because the existence of such endophytic forms was 

 at that time regarded as establishing a presumption in favour of 

 spontaneous generation. 



The Zeitschrift jiir IVissenschaftliche Botanik, 1844-46, is a 

 very remarkable publication. It never got beyond its first 

 volume, but it may be doubted whether any book of its size 

 has been more important for the progress of the science. 

 Nageli's introductory paper, " Ueber die gegenwartige Aufgabe 

 der Naturgeschichte, insbesondere der Botanik," is very meta- 

 physical in tone, and is not free from a certain youthful pedantry. 

 Great stress is laid on the absolute difference of species — a con- 

 ception which, as Nageli tells us in one of his later works, did 

 not prevent his believing even then in the origin of species by 

 descent. The study of development is treated as a philoso- 

 phical necessity, and anatomy, or the study of mature structure, 

 is denied to be a science. This is perfectly just ; no one did 

 more for anatomy than Nageli himself, but he recognized that it 

 only becomes scientific in unionwith development and physiology. 

 He further insists that the knowledge of development as a whole 

 is the only sound basis for classification — a principle which still 

 remains to be carried out. The highest importance is attached to 

 the cell theory, which was expected to do as much for botany 

 and zoology as mathematics had done for physics, or atomic 

 formula: for chemistry — an expectation which cannot be regarded 

 as unjustified. Nageli severely criticized the theories then 

 current, according to which cell-formation is a process of 

 crystallization. Some of the most doubtful of his own later 

 generalizations, however, were affected by the same source of 

 error — namely, too great eagerness to find a simple physical 

 explanation for biological phenomena. 



Nageli, in this paper, devotes much space to the distinctions 

 between animals and plants. He decisively rejects the idea of 

 a transition between the two kingdoms, on the ground that this 

 would contradict the " Absolutheit der Begriffe" — an argument 

 which now seems strangely out of place in natural science. 



The whole paper is of great interest as showing the point of 

 view from which biological questions were regarded at that time 

 by a brilliant and philosophical naturalist just entering on his 

 life's work. 



The two papers in the Zeitschrift, on the nuclei, formation 

 and growth of vegetable cells (1844 and 1846), are of the 

 greatest importance to histology, finally establishing the constant 

 occurrence of cell-division as the one mode of vegetative cell- 

 formation. This conclusion was only reached in its complete- 

 ness in the second of the two papers. Although Unger's and 

 Mohl's views of the details of the process were in some respects 

 the more correct, still Nageli established the main facts of the 

 division of the nucleus and of the cell on a broad basis of 

 observation. These papers, as well as one on the utricular 

 structures in the contents of cells (nuclei, nucleoli, chloro- 

 phyll granules, &c.) were translated by Henfrey for the Ray 

 Society, to the great benefit of English students, as the writer 

 of this article can testify. 



In the same journal there are several algological papers, the 

 most important of which is the complete and admirable account 

 of Caulerpa prolifera, the extraordinary histological structure of 

 which and its relationship to the other Siphonese Nageli already 

 thoroughly understood. It is interesting that in this paper he 

 describes both the cell-wall and the cellulose rods as growing by 

 apposition, a view to which we have now returned, owing to the 



NO. I 146, VOL. 44 1 



observations of Strasburger and Noll, in opposition to Nageli's 

 own later theory of intussusception propounded in 1858. 



The paper on Delesseria hypoglosstim contains an elaborate 

 account of the cell-divisions by which the thallus is built up. 

 Nageli here characteristically attributes great importance to the 

 introduction of ideas of absolute mathema.ical form into 

 physiology and systematic botany. 



The discovery of spermatozoids in the Ferns is one of the 

 most important recorded in this voluna. The essential points 

 in the structure and development of the antheridia are described 

 rightly, and the movements of the sparmatoziiis very accurately 

 traced. Nageli calls attention to the nuclear re ictions of the 

 substance of the spermatozoids. He demonstrates the homology 

 of these bodies with those of the misses ani Chara and of 

 animals. Nii^eli was at that timj necessarily completely in the 

 dark as to the relation of the spermatozoids to spore formation, 

 for the arch'-gonia and the pro>:ess of fertilization were first dis- 

 covered by S iminski four years later. 



Among other papers of fundamantal importance may be 

 mentioned that on the growth of mjsses, in which the apical 

 cell-divisions and the development of the protonemi are clearly 

 made out ; that on the growth of the stem in vascular plants, 

 a work which laid the foundation of our knowledge of the dis- 

 tribution of vascular bundles, and that on the reproduction of 

 the Rhizicarps. This last is especially interesting. It is 

 directed, though very cautiously, ajainst the Schleidenian theory 

 of fertilization as applied to these plants. It is singular how 

 this theory, according to which the end of the pollen-tube, after 

 penetrating the embryo-sac, itself baca-ne the embryo, took 

 possession of the minds of botanists at that tims, and led some- 

 times to the strangest confusions, sometimes to a chance re- 

 cognition of homologies, which couldoaly be legitimately proved 

 at a later period of research. In the case of the Rhizocarps, 

 the Schlei ienian theory assumed that these plants were really 

 Phanerogams. Hence we find that he and Nageli agree in 

 calling their microspores pollen-grains, their microsporangia 

 anthers, their macrospo:es embryo-sacs, and their macrospor- 

 angia ovules, a terminology which very nearly expresses ou* 

 present view of their homologies as established by Hofmsister. 

 Nageli discovered the spermatozoids of these plants as well as 

 the prothallus and archegonia, but he shows the greatest reserve 

 in correcting Schleiden's extraordinary mistakes. 



It is worth remarking that at this early period the homology 

 of pollen-grains with spores was generally admitted, and at 

 first we wonder how this true result could have been arrived at 

 so prematurely. Here again the Schleidenian theory affords the 

 explanation. The pollen-grain was regarded as a spore, which 

 on germination produced the embryo-plant, not as do the spores 

 of Cryptogams in the open air, but within the embryo-sac of th ^ 

 ovule. This conclusion was of course strengthened by a more 

 legitimate ar^^umant drawn from a comparison of the mode of 

 origin of pollen-grains and spores. 



A less fortunate result of the same theory appears in a paper 

 in the Zeitschrift, " Ueber das Wachstum und den Begriff des 

 Blattes." Nageli here erroneously attributes to the stem and 

 its branches an endogenous origin. That this holds good for the 

 primary axis, he proves by stating that it is derived from the 

 pollen-grain, which itself arises endogenously within the anther \ 



We have dwelt long on this Zeitschrift, as it affords a remark 

 able insight into the state of botanical questions during the earlier 

 part of the most brilliant period of progress which the science 

 has known. The very name. Journal for ^^ Scientific" Botany, is 

 characteristic, expressing the somewhat arrogant claims of the 

 enthusiastic naturalists of the new school of that day. 



The next period in Nageli's career is marked by the publi- 

 cation of two important algological works : "Die neueren Algen- 

 systeme und Versuch zur Begriindung eines eigenen Systems der 

 AlgenundFlorideen," 1847, and "Gattungeneinzelliger Algen," 

 1849. It cannot be said that Nageli was altogether happy in 

 his generalizations on algological su'ojects, though his special 

 work was often of the greatest value. At that time he included 

 the Lichens among the Algae and excluded the Florideae. The 

 Algat in his sense were distinguished from the Fungi, not only 

 by the presence of chlorophyll and starch, but also by the absence 

 of spontaneous generation, while they differed from the Floridea; 

 and all the higher plants in being destitute of sex. The Florideae, 

 on the other hand, he regarded as sexual and as closely allied to 

 the Mosses. He recognized their antheridia as the male organs, 

 but regarded the tetraspores as the product of a female organ, 



