TRANS AQTIONS OF SECTION K. 937 



The polar nuclei of this plant unite before fertilisation, but that there is no 

 absolutely fixed period is shown by the very difiFerent appearance of sacs in which 

 polar fusion is taking place. 



The male generative nuclei, when first set free in the embryo sac, are extremely 

 small and heavily stained. Their chromatic substance is so densely aggregated as 

 to render the spermatozoid to all appearance homogeneous. 



Of the two spermatozoids one — I believe that which leaves the pollen tube 

 first — passes to the middle of the sac and there fertilises the definitive nucleus ; the 

 other fertilises the nucleus of the oosphere. 



By the time the male generative nucleus or spermatozoid has reached the 

 definitive nucleus, it has enlarged immensely, and shows a light spongy structure 

 with scattered chromatin granules. The other spermatozoid, however, increases 

 very little in size, and always remains dark and dense. 



When the .spermatozoids leave the pollen tube they are somewhat short and 

 thick, and only slightly curved, but when the one has approached the definitive 

 nucleus, it has the typical vermiform shape, with one or several coils. 



Professor Nawaschiu has recently published an account of double fertilisation 

 in JJelphinium and in two Composites. 



2. The Conducting Tissues of Bryophytes. By A. G. Tansley. 



The most important part of our present knowledge of these tissues is due to 

 Haberlandt,' who, in the Poly trichacese, distinguished a hadrom (hydroon) or water- 

 conducting system from a leptom, conducting plastic, especially nitrogenous, sub- 

 stances. In the lower mosses, only the hydrom is differentiated, and in the 

 xerophilous and hydrophilous forms, in which water is taken in at any part of 

 the surface, even this is absent. Localisation of the region of absorption is the 

 condition on which the evolution of a hydrom depends. 



In the present investigation the lignified strand of proseuchyma in the midst of 

 the thallus of certain Liverworts {Pallamcinia.Symphyoyyna and Hymenophytoti) 

 was shown to be a hydrom strand, and its development to be correlated to some 

 extent with the localisation of the absorptive region of the thallus. 



The rhizome of four species of Po(y^nc^2<7?i was investigated, and in every case 

 was found to possess with striking completeness the distribution of tissues 

 characteristic of the root of a vascular plant. The transition to the structure of 

 the aerial stem was followed, and while the account of the structure of the latter 

 given by previous observers was confirmed in most particulars, some new points in 

 the structure and course of the leaf-traces were observed, and new light was, it is 

 hoped, thrown on the constitution of the Polytrichaceous stele, which is thought to 

 consist of two regions, primitively distinct in function and by descent. Finally, 

 an attempt has been made to trace out the course of evolution of these conducting 

 tissues in the Bryophytic series. 



3. On a Fourth Type of Transition from Stem to Root- structure occur 

 ring in certain Monocotyledonous Seedlings. By Ethel Sargant. 



The three types of transition from a stem to a root-structure described by 

 Professor Ph. van Tieghem (' Traite de Botanique,' 12me edition, 1891, p. 782) are 

 briefly as follows : — 



1. As the n bundles of the hypocotyledonary stele descend mto the primary 

 root, the xylem of each bundle branches to right and left at the same time that 

 the protoxylem elements become external. The right-hand branch from each 

 bundle unites with the left-hand branch of the adjacent one, so that we still have 

 n xylem groups in the root-stele. The n phloem groups descend in a straight 

 line without branching or rotation. 



' Beitrdge zur Anatomie und Physiologie der Lauhnoose, 188G. 



