ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 201 



In reply, A. Tscbirch* gives farther details of the resinogenous layer 

 in the leaves of conifers, which is frequently difficult to detect, and is 

 often entirely resorbed at maturity. 



Mucin.f — B. Schroder reviews the researches that have been made 

 respecting the pectinaceous substances formed by plants and the muci- 

 lages by animals, and concludes tbat there is a very close resemblance, 

 if not an identity, between vegetable mucin and that of animals. 



(3) Structure of Tissues. 



Structure of Vascular Plants.J — G-. Chauveaud points out the mode 

 of formation of the primary structures (protoxylem), intermediate struc- 

 tures (metaxylem), and secondary structures, in the root of vascular 

 plants. Take such an example as the radish — there are found at the 

 base of the cotyledons the same structures as in the root, the difference 

 consisting in a reduction of the protoxylem, and a more rapid succession 

 of the different structures. They are less often to be found in the stem 

 and in the leaf, because the arrest of the development of the protoxylem 

 is, in most plants, manifested at a lower level. 



" Bicollateral Bundles."§ — J. Baranetzky contests the accuracy of 

 the term " bicollateral " as applied to the vascular bundles of dicotyle- 

 dons, whether looked at histologically or from the point of view of their 

 development. Bundles may be complete, i.e. composed of both xylem 

 and phloem, or incomplete, composed of phloem alone. It is only in the 

 Cucurbitaceae and the Melastomaceae that we get bundles which have on 

 their inner margin a second group of phloem embracing the xylem as 

 does the external phloem. In other families the bundles of internal 

 phloem are always separated from the xylem by a more or less thick 

 layer of parenchyme, and form an autonomous system altogether inde- 

 pendent of the normal bundles, and capable of increasing in thickness 

 by the activity of a unilateral cambium of their own. In Mumex, Bheum, 

 and some other genera, the bundles of the inner ring are complete in 

 the centre of their length, but become gradually incomplete towards 

 their two extremities. In Campanula the structure of the bundles varies 

 within the genus. In the Solanaceae, Asclepiadeae, Apocynaceas, Myr- 

 taceaB, Convolvulaceaa, and other orders, the internal bundles never form 

 xylem. 



The true nature is then described in detail of the vascular structure 

 in a number of natural orders in which " bicollateral " bundles were said 

 to exist. In all cases the inner bundles originate from the zone of 

 active meristem which produces the normal bundles. The formative 

 cambium ring merely represents an outer layer of the central cylinder, 

 which only gradually loses its properties towards tbe centre of the stem. 

 The appearance of inner vascular bundles in dicotyledons is not an 

 anomalous, but a normal phenomenon. 



Function of Laticifers. || — L. Gaucher reviews the arguments in 

 favour of the two views tbat have been held respecting the function of 



* Ber. Deutsch. Bot. Ges., xix. (1901) pp. 25-32. 



t Beih. a. Bot. Centralbl., x. (1901) pp. 121-4. 



X Comptes Rendus, cxxxii. (1901) pp. 93-5. 



§ Ann. Sci. Nat. (Bot.), xii. (1900) pp. 261-332 (4 pis.). 



|| Tom. cit., pp. 241-60 (9 figs.). 



