EMBRYOLOGY OF GYMNOSPERMS. 75 1 



means of motile antherozoids ceases. The fertilising material — and this is the 

 only essential in the matter — is carried to the oosphere in quite another manner, 

 namely, by the male microspores (which are distinguished in the Phanerogams 

 as pollen-grains) fixing themselves to a portion of the female organ of reproduction, 

 and thence emitting a tubular prolongation, which makes its way through the tissue- 

 masses surrounding the oosphere, and finally penetrates to the oosphere, to which 

 it subsequently transmits the male fertilising substance. This tube is called the" 

 Pollen-iube. 



It is unfortunately necessary to add here a few definitions of terminology, since the 

 history of our science has brought it about that organs of like kind in different classes 

 of plants, in spite of their homology, were previously held to be essentially different 

 and have therefore had different names assigned to them. At the present time, when 

 we perceive clearly the true connection of these matters it would be possible, and is 

 demanded in the interest of science, to designate the pollen-grains simply microspores, 

 and the embryo-sac simply the macrospore, in order to indicate their homologies; never- 

 theless the old nomenclature can now scarcely be entirely put aside, since it is too 

 deeply fixed in the literature, so that to the uninitiated doubts might arise as to the 

 meanings of terms in reading different books. 



As already mentioned, the gymnospermous plants (Coniferse, Cycadese, and 

 Gnetaceae) are directly allied in their reproductive processes to the higher Cryptogams 

 with two kinds of spores : nevertheless this was by no means an easy matter to 

 establish. The investigations of many years were needed to arrive at this conclusion. 

 If I quote a few examples, it will be at once seen that the essential and important 

 points are not directly obvious. 



The facts of fertilisation come out particularly clearly in the case of the Yew 

 (Taxus baccata). Each Yew-tree is either entirely male or entirely female, and 

 thus it is only trees of the latter kind which bring forth the seeds, which are found 

 in autumn surrounded by an elegant i:ed thick envelope. The male and female 

 trees flower in the spring. The male flowers are situated on the under side of the 

 horizontal lateral shoots of the tree : ■ they are small buds {A Fig. 436) bearing 

 numerous minute scale-leaves at their lower parts, and at the apex eight to ten 

 peculiarly formed structures a which remind one forcibly of the sporangiophores 

 of Equisetum. A stalked disc bears on its under surface four or five pollen-sacs, 

 which may be forthwith designated sporangia ; when these open, they set free their 

 microspores, which however are generally known as pollen. 



On the female Yew trees also minute bud-like shoots are found in the spring 

 on the lower side of horizontal branches (C, Fig. 436). Here also numerous 

 scale-leaves j are present ; anteriorly, however, is a peculiar projecting structure s k. 

 This is the Ovule, so termed beca;use the seed containing the embryo is developed 

 from it after fertilisation. Fundamentally, however, this ovule is simply a very 

 highly developed macrosporangium, as will be more clearly seen later on. It 

 will also be well to regard more closely the longitudinal section through the whole 

 female shoot D. Here is seen the ovule at the apex of the shoot, and it is observed 

 that it consists of two diflFerent structures. The approximately hemispherical body- 

 K R \% the so-called Nucellus of the ovule, and it constitutes the essential part : 

 this is the proper macrosporangium, m. which the so-called embryo-sac or macrospore 



