924 REPORT— 1900. 



hj ■which the cells are multiplied — in opposition to the Schleidenian theory of free 

 cell-formation — early sugs-ested doubts as to the propriety of re;?ardiDg the body as 

 being built up of cells as a wall is built of bricks. Later the minute study of the 

 Thallophyta revealed the existence of a number of plant?, such as the Myxomycetes, 

 the phycomycetous Fungi, and tlie siphonaceous Algos, some of them highly 

 organised, the vegetative body of which does not consist of cells. It became clear 

 that cellular structure is not essential to life ; that it may he altogether absent or 

 present in various degree. Thus in the higher plants the protoplasm is segmented 

 or septated by walls into uninucleate units or 'energids' (Sachs), and such plants 

 are well described as ' completely septate.' But in others, such as the higher Fungi 

 and certain Algie (e.g., Cladophora, Hydrodictiion), the protoplasm is septated, not 

 into energids, but into groups of energids, so that the body is ' incompletely 

 septate.' Finally there are the Thallophyta already enumerated, in which there is 

 complete continuity of the protoplasm : these are ' unseptate.' Moreover, even 

 when the body presents the most complete cellular structure, the energids are not 

 isolated, but are connected by delicate protoplasmic fibrils traversing the inter- 

 vening walls ; a fact which is one of the most striking discoveries in the depart- 

 ment of histology'. This was first recognised in the sieve-tubes by Hartig (1837) ; 

 then by Naegeli (1846) in the tissues of the Florideaj. After a long period of 

 neglect the matter was taken up once more by Tangl (1880), when it attracted the 

 attention of many investigator.?, as the result of whose labours, especially those of 

 Mr. Gardiner, the general and perhaps universal continuity of the protoplasm in 

 cellular plants has been established. Hence the body is no longer regarded as an 

 aggregate of cells, but as a more or less septated mass of protoplasm : tlie synthetic 

 standpoint of Schwann has been replaced by one as distinctively analytic. 



Time does not permit me to do more than mention the important discoveries 

 made of late j-ears, mainly on the initiative of Strasburger, with regard to the 

 details of cytology, and especially to the structure of the nucleus and the intricate 

 dance of the chromosomes in karyokinesis. Indeed, I can do but scant justice to 

 those anatomical discoveries which are of more exclusively botanical interest. One 

 important generalisation which may be drawn is that the histological differentia- 

 tion of the plant proceeds, not in the protoplasm, as in the animal, but in the cell- 

 wall. It is remarkable, on the one hand, how similar the protoplasm is, not only 

 in different parts of the same body, but in plants of widely diflerent affinities ; and, 

 on the other, what diversity the cell-wall offers in thickness, chemical composition, 

 and physical properties. In studying the differentiation of the cell-wall the 

 botanist has received valuable aid from the chemist. Research in this direction 

 may, in fact, be said to have begun with Payen's fundamental discovery (1844) 

 that the characteristic and primary chemical constituent of the cell-wall is the 

 carbohydrate which he termed cellulose. 



The amount of detailed knowledge as to the anatomy of plants which has been 

 accumulated during the century by countless workers, among whom Mohl, Naegeli, 

 Unger, and Sanio deserve special mention as pioneers, is very great — so great, 

 indeed, that it seemed as if it must remain a mere mass of facts in the absence of 

 any recognisable general principles which might serve to m.arshal the facts into a 

 science. The first step towards a morphology of the tissues was Hanstein's investi- 

 gation of the growing point of the Phanerogams (1868), and his recognition therein 

 of the three embryonic tissue-systems. This has lately been further developed by 

 the promulgation of van Tieghem's theory of the stele, which is merely the logical 

 outcome of Hanstein's distinction of the plerome. It has thus become possible to 

 determine the homologies of the tissue-systems in different plants and to organise 

 the facts of structure into a scientific comparative anatomy. It has become appa- 

 rent that, in many cases, differences of structure are immediately traceable to the 

 influence of the environment; in fact, the study of physiological or adaptive 

 anatomy is now a large and important branch of the subject. 



The study of Anatomy has contributed in some degree to the progress of 

 systematic Botany. It is true that some of the more ambitious attempts to base 

 classification on Anatomy have not been successful ; such, for instance, as de 

 CandoUe's subdivision of Phanerogams into Exogens and Endogens, or the subdivision 



