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FOURTH GROUP. 



loosely along an axis, as in a catkin. The axis is often elongated and slenderer below 

 the torus, and is either naked or furnished with one or two small leaflets or bracteoles ; 

 this part of the axis is the flower-stalk ox peduncle ; if it is very short the flower is said 

 to be sessile. As a rule no shoots are formed in the axils of the floral leaves, even 

 though the plant produces shoots in the axils of all the other leaves ; yet abnormal 

 cases of axillary branching inside the flower are not altogether uncommon. 



The Jtiale spores {microspores or pollen-grains) are produced in microsporangia, 

 which may be generally termed pollen-sacs ; these are at first bodies of solid tissue, in 

 which, as in other sporangia, a hypodermal archesporiitm is differentiated, while the 

 surrounding layers of tissue become the wall of the pollen-sac. It has been already 

 stated, that the mother-cells of the pollen-grains cease to form a connected tissue and 

 become isolated, though this is not always the case, and then form the pollen-grains 

 by division into four parts ; a more detailed account of these processes will be found in 

 the description of the separate classes, but something must be said here respecting the 

 morphology of the pollen-sac. The pollen-sacs of the Phanerogams, like the sporangia 

 of most Vascular Ciyptogams, are commonly the product of leaves (sporophylls) ; 

 but in the Phanerogams these leaves usually undergo a striking metamorphosis, and 

 remain as a rule much smaller than the other leaves ; a leaf which bears pollen-sacs 

 may be termed a staminal leaf or stameti (androphyll). Modern research has discovered 

 cases in which the pollen-sacs spring from the elongated floral axis itself, as in Naias 

 according to Magnus, in Casuarina according to Kaufmann, and in Typha according to 

 Rohrbach. In the Cycadeae the pollen-sacs are found singly or in groups {sori) on 

 the under side of relatively large staminal leaves, and often in large numbers, like the 

 sporangia on the leaves of Ferns. In the Coniferae the staminal leaves already cease 

 to look like ordinary leaves ; they continue small and form several or only two com- 

 paratively large pollen-sacs on the under side of the lamina which in most cases may 

 still be distinguished. In the Angiosperms the staminal leaf is usually reduced to a 

 delicate stalk-like supporter, which is often of some length and is termed \\vq filament ; 

 it bears at its upper extremity, or beneath it on both sides, two pairs of pollen-sacs 

 which are together reckoned as one whole under the name of anther \ the anther 

 therefore consists usually of two longitudinal lobes, which are at once connected and 

 separated by a part of the filament called the connective. The two pollen -sacs of each 

 anther-lobe are united longitudinally to one another, and the two lobes are also not 

 unfrequently combined into a single whole. In this case the pollen-sacs appear as 

 compartments of the anther, which is then said to be quadrilocular as distinguished 

 from bilocular anthers, of much less frequent occurrence, in which each lobe consists of 

 a single pollen-sac. 



The embryo-sac, the maa-ospore, is formed in the manner indicated above in the 

 central tissue of the macrosporangium (ovule) named the micellus. The nucellus, usually 

 ovoid in shape, is composed of small-celled tissue, and is almost always enclosed in 

 one or two envelopes each formed of a few layers of cells ; these envelopes, the integu- 

 ments, grow up round the young nucellus from its base, and becoming narrower at its apex 

 and extending often some way above it form there a canal-like passage, the micropyle, 

 through which the pollen-tube forces. its way in order to reach the apex of the nucellus 

 and ultimately the apex of the embryo-sac. In many cases the nucellus surrounded by 

 its integuments is borne on a stalk, xhe. funiculus ; this is sometimes wanting and then 

 the ovule is sessile. The funiculus is with rare exceptions, as in the Orchideae, traversed 

 by a vascular bundle which usually terminates at the base of the nucellus, as happens 

 also in the sporangia of Botrychiutn. The outward form of the ovule when ready for 

 fertilisation varies much ; there may be outgrowths of several kinds on the funiculus 

 and integuments, but of special importance is the direction of the nucellus and its inte- 

 guments with respect to the funiculus. The ovule is straight or ortJiotropous when the 

 nucellus appears as a prolongation of the funiculus in the same straight line, and its 

 apex forms the apex of the entire ovule ; but it is much more often ini'crted or anatropous, 



