GROUP IV. GYMNOSPERM.S. 421 



General histological peculiarities. In all the Coniferae, except 

 Taxus, resin-ducts (see p. 98) are present : they are always to be 

 found in the leaves and in the cortex of the stem, sometimes also 

 in the pith of the stem (Ginkgo), in the primary wood (Finns, 

 Larix), or in the primary bast (Araucaria) : they are absent from 

 the root in many genera, and when present they never occur in the 

 cortex, but are situated in the primary wood (Pinus, Larix), in the 

 primary bast (Araucaria), or as a single canal in the centre of the 

 conjunctive tissue (Cedrus, Abies) : they are formed also in the 

 secondary wood (Pinus, Picea, Larix) or in the secondary bast 

 (Cupressus, Thuja), of both stem, and root. Mucilage-ducts re- 

 sembling the resin-ducts of the Coniferae, occur in the cortex of the 

 stem in the Cycadacese. 



The bast of the Gymnosperms resembles that of the Pterido- 

 phyta, and differs from that of the Angiosperms, in that it contains 

 no companion-cells (see p. 96), the function of these cells being 

 performed by certain cells belonging either to the medullary rays 

 (Abietineae, some Cupressineae) or to the bast-parenchyma. 



The General Morphology of the Reproductive Organs. 

 The reproductive organs are microsporangia (pollen-sacs) and macro- 

 sporangia (ovules) : the microsporangia are borne- on sporophylls, but 

 (except Gnetum) the macrosporangia are sometimes borne directly on 

 the axis (e.g. macrosporangia of Taxeae and of the Gnetaceae) : they 

 are developed on distinct shoots, and frequently on distinct plants 

 (e.g. Cycadaceae : some Coniferae, such as the Taxeae ; Gnetaceae 

 generally). 



Certain shoots, are more or less clearly differentiated as floiccrs ; 

 the only exception being Cycas in which there is- no proper macro- 

 sporangiate flower. The flower is always unisexual : its structure 

 varies widely ; it may consist merely of a terminal sporangium 

 invested by a few small bracts (e.g. macrosporangiate flower of 

 Taxeae) ; of a terminal sporangium with a rudimentary perianth 

 (macrosporangiate flower of Gnetaceae) ; of one or more sporophylls 

 borne on a short axis and surrounded by a perianth (micro- 

 sporangiate flower of Gnetaceae) ; or of a larger or smaller number 

 of sporophylls arranged on an elongated axis, the- whole forming a 

 cone. 



The SporophylU are of two kinds, distinguished by the nature 

 of the sporangia which they respectively bear, as microsporophylls 

 and macrosporophylls. When the flower is a cone, the sporophylls. 

 have a general resemblance to scaly leaves: in other flowers- 



