318 ME. W. C. WOESDELL ON " TEANSFUSION-TISSUE." 



those genera which approach nearest to Ginkgo in general relationship, such as 

 Cephalotaxus and Taxus. In many genera, however, no trace of this tissue could 

 by discovered, at least in the sections examined, though it is not improbable 

 that isolated remnants of it may occur here and there along the course of the 

 bundle through the leaf. 



4. The occurrence, in the cotyledonary bundles of Ginkgo hiloha, Linn., and Cycas 



revoliita, Thunb., of an intimate union and gradual transition between the 

 tracheides of the centripetal xylem on the one hand and those of the trans- 

 fusion-tissue on the other; whence it may be justly inferred that the latter 

 tissue owes its origin, wherever it may subsequently be found, directly to the 

 former. Though in the leaves of the majority of Coniferae this origin is by this 

 time almost entirely obscured, owing to the more or less complete obliteration of 

 the centripetal xylem, it is still often evidenced by the presence of transfusion- 

 tissue on the ventral side of the xylem, by the very frequent extension of the 

 lateral transfusion-tissue towards the ventral side of the bundle^ and by the 

 transitions in the characters of the tracheides between those most externally 

 placed and those nearest the protoxylem. In the foliage-leaves of Cycas the 

 connection between the two tissues is obvious. 



5. The final inference, that transfusion-tissue, wliich occurs almost universally in the 



leaves of Gymnospermous plants as an auxiliary conducting-system, has been 

 phylogenetically derived from the ceatripetally-formed xylem of the vascular 

 bundle, and is thus, morphologically, an integral portion of the bundle itself. 



I am indebted to Mr. C. P. Robertson-Glasgow for the use of some excellent 

 preparations of the cotyledons, leaves, &c., of various Coniferous plants. My best 

 thanks are also due to Dr. D. H. Scott for many invaluable criticisms and much 

 kind assistance during the progress of my work. 



[The important discovery, quite recently made by the two Japanese botanists, Hirase 

 and Ikeno, of spermatozoids in the pollen-tubes of Cycas revoluta, Thunb,, and Ginkgo 

 hiloba, Linn., and still more recently by Webber in a species of Zamia, bridges over in a 

 striking manner the gulf, hitherto supposed to exist between flowerless and flowering 

 plants, between Ferns or Fern-like plants and Gymnosperms. The relation between the 

 two great groups of plants had already been partly indicated by the Fern-like foliage of 

 such a Cycad as Stangeria. 



One of the most important of the facts brought forward in the present paper, viz. the 

 occurrence of centripetal xylem in the cotyledonary bundles of both Ginkgo biloba, Linn., 

 and Cycas revoluta, Thunb., seems to me (especially in view l)oth of the external characters 

 and anatomical structure of such fossil forms as the Mcdullosece, Lyginodendron, and 

 Nceggerathia) to strongly support the above conclusion that Ginkgo and the Cycads hold 

 an intermediate position between soms primitive group or groups of Fern-like plants and 

 modern Gymnosperms. 



1st October, 1897. W. C. W.] 



