6D2 



NATURE 



{Oct. 28, 1880 



a voluminous treatise. But such treatment of the subject 

 has a very high educational value and a certain ethical 

 importance. 



Further, it may be noted that the author has neces- 

 sarily a difficulty to contend with in the scope itself of 

 his book. Embryology is not a natural nor a convenient 

 division of biological science. The study of the orga- 

 nism in its complete form cannot be advantageously 

 separated from the study of the coming about of that 

 form, and indeed it is very difficult for a writer who pro- 

 poses to himself to describe the developmental changes 

 of organisms to draw the line consistently in the various 

 cases which he describes, and to say that at such a point 

 his business with the organism ceases and that of the 

 "antipjedologist " begins. It is because the knowledge 

 of embryological facts is to so large an extent new, that 

 separate treatises on embryology are necessary. It is as 

 a supplement to treatises on the structure or anatomy of 

 animals which do not sufficiently deal with embryology 

 that such a distinct treatise is needful, and such need is 

 merely the result of the late development of embryo- 

 logical research. 



In the course of time w-e shall no doubt see a complete 

 fusion of "embryology" and " antipasdology " — the facts 

 of structure to be observed in the youth and in the 

 maturity of organisms being treated as a matter of course 

 concurrently. Nothing could conduce more ^directly to 

 this desirable state of things than the really remarkable 

 and successful effort which Mr. Balfour has made to 

 gather together and present in a compact and logical 

 form the embryological results which have been and still 

 are pouring forth from Russian, German, English, French, 

 and American laboratories in an overwhelming stream, 

 calculated to daunt by its velocity any but the most 

 determined student. E. Ray Lankester 



THE SIEVE-TUBES OF DICOTYLEDONOUS 



PLANTS 

 Bcitrdge sur Kenntniss des Siebrohrenapparates dicolyler 



Pflanscn. Von Dr. Karl Wilhehn. (Leipzig : W. 



Engelmann, 1880.) 



IT is perhaps natural, owing to its pecuharities, and 

 especially to the character of the cell walls, that the 

 soft bast was comparatively lately investigated and 

 described ; ' but it is surely a surprising fact that the 

 ground should have been left open till the present year, 

 for a thorough investigation of the development of those 

 tissues which are characteristic of the phloem. 



In the " Comparative Anatomy " of De Bary ^Ye find a 

 full account of what was known in 1877 of the structure 

 and development of the soft bast ; at the same time the 

 writer pointed out several questions concerning which 

 further investigation was required. He drew especial 

 attention to our want of knowledge of the relation of the 

 cambiform cells - to the sieve-tubes, and of the develop- 

 ment of the sieve plale, the callus mass, and the contents 

 of the sieve-tube. It has been the object of Dr. Wilhelm's 

 researches to supply information on these several points ; 



' The sieve tubes were discovered by H,-irtig (1837). His observ.-itioiis 

 5;?.f* ,'."""y y«^"'s ••'fler verified by other observers, especially von Mohl, 

 Ivageli, :ind Hansteiii. 



- Dc B.iry, "Vcrgl. Arat.," p. 337. 



while at the same time he affords us many other interesting 

 details. 



Owing to the wideness of the subject it was impossible 

 for the author to e.xtend his researches beyond a limited 

 number of types. Those selected were Vilis viiiifcra, L., 

 Ctircubita pepo, L., and Lagenaria vulgaris, Ser. It will 

 be seen that Dr. Wilhelm has selected plants having 

 sieve-tubes of the two different types common among the 

 Dicotyledons, viz., Cucurbita and Lagenaria where the 

 structure is more simple, Vitis where it is complicated by 

 the presence of several sieve-plates side by side on the 

 same cell wall. In a note at the end of the paper the 

 author specially asserts that his results only apply to the 

 plants named ; while further research must show whether 

 the structure described is really typical. 



The main results arrived at are as follows : — Those 

 formative cells of the bast which are set apart for the 

 development of a member of a sieve-tube, usually suffer a 

 longitudinal division into two unequal cells : the larger 

 forms one member of the sieve-tube ; the other, which is 

 smaller and shorter, develops into the companion-cell 

 (GcL'itsclle). The latter may, in Cucurbita and Lagenaria, 

 again divide. The walls separating the companion-cells 

 from the sieve-tube are fitted, and the cell contents richly 

 protoplasmic. It will be seen that these cells, being sister 

 cells of the members of the sieve-tubes, must be dis- 

 tinguished from the larger cells, which are usually termed 

 " cambiform ; " these latter being formed by division from 

 formative cells of the bast, but not being in direct genetic 

 connection with the cells, which develop into members of 

 the sieve-tubes. 



Dr. Wilhelm finds that the " callous " condition of the 

 sieve-plate is not, as previously supposed, the result of a 

 secondary change of the plate ; on the contrary, the dif- 

 ferentiation of the sieve-plate begins by the change of the 

 cellulose to "callus" at a number of points. It is in the 

 callus masses, formed at these points, that the pores of 

 the sieve later appear. The callus may extend itself from 

 these points so as to cover the whole face of the plate, 

 and completely inclose the cellulose sieve. A callus- 

 skeleton is thus formed which may be isolated. 



The callus varies in volume, increasing with age, or on 

 approach of the period of rest ; in which case the pores 

 iTiay be completely stopped ; or decreasing as the period 

 of summer activity approaches, when the pores are again 

 opened. This result may be obtained by artificial means. 

 It is best seen in Vitis ; it is probable that this variation 

 of volume of the callus is by no means universal. 



As regards the substance of the callus it will be seen 

 from the following reactions that it cannot be identified 

 with any of the substances previously described. With 

 acids and alkalies it swells quickly ; if the reagents be 

 strong it is dissolved. Ammoniacal sub-oxide of copper 

 attacks it only slightly, or not at all ; by use of this 

 reagent the callus-skeletons before mentioned may be 

 obtained free. Solution of iodine in alcohol does not 

 colour it ; solution of iodine in potassium iodide colours 

 it yellow to brownish yellow. This with Schultz's solution 

 gives a deep red brown ; when used alone the latter 

 reagent gives no colour, but causes considerable swelling. 

 Thus far w'c have only discussed the cell walls. While 

 the development of the sieve has been going on, but 

 before the perforations are formed, a change appears in 



