20 SPORES AND THALLIDIA. 



term used is apotheciuvi. Perithecia and apotliecia have been erroneously called 

 fruits also. The same principles must here be applied as governed our consideration 

 of Ferns and Mosses. Even if the genesis of perithecia and apothecia is really 

 preceded by a process of fertilization, still the only part properly to be called 

 a fruit is the tissue in which one or more protoplasts have become embryos in 

 consequence of the act of fertilization. The outgrowth from this fruit is precisely 

 the new generation; and it does not matter at all whether this new sporogenous 

 generation preserves its connection with the previous fruit-forming generation 

 or not. Perithecia and apothecia, and, in general, all so-called fruits in the 

 Ascomycetes are therefore equivalent to the sporogonia in Bluscinese and to the 

 spoi'angiferous plants in Horse-tails, Club-mosses, and Ferns. 



We shall place together in a third group all spores which arise neither singly 

 in the cell-compartments of a tissue nor through the breaking up of the protoplasm 

 within a tube, but by abstriction and abjunction. The process of spore-formation 

 in these cases is as follows: — The protoplasm, which is inclosed in a cell-wall, 

 produces an internal partition whereby it is itself divided into two halves, and the 

 cell-cavity into two chambers. As soon as this has taken place the partition-wall 

 splits and the two cells fall asunder. If the cell which undergoes the process 

 of bipartition is in the form of a blind tube or sac, and if the partition is inter- 

 calated near the tip of the sac, the effect produced is as though the end of the sac 

 had been tied off or abstricted and had then dropped. The part remaining behind 

 now constitutes another blind sac, and in some genera the process of abjunction 

 from the extremity may be repeated over and over again. Basidium is the name 

 given to a closed sac of this kind from which spores are abstricted, it forming 

 in a manner a base for the spores. This term has hitherto only been employed by 

 botanists in relation to the so-called Basidiomycetes (which includes the Fungi 

 known as Mushrooms and Toadstools), but it is justifiable to extend its application 

 to all other structures which play the same part. 



Abstriction of spores is exhibited at its simplest in the plant known as the Rust 

 of Wheat, which at a certain stage of its development lives as a parasite in the 

 green tissue of the leaves of our species of Wheat. For the purpose of spore- 

 formation tufts of hyphse project beyond the surface of the infested leaves. At 

 the extremity of each hypha, which is in the form of a closed sac, a single spoi'e 

 of comparatively large size is developed; and after the fall of this one spore the 

 hypha or basidium has lost the power of abstricting others. 



A similar phenomenon is observed in the Fungi belonging to the genera 

 Hydnwm, Polyporus, Agaricus, and Clavaria, of which several examples are 

 represented in fig. 195. Their basidia are club-shaped, and terminate in four 

 slender filaments, the so-called sterigmata, and from the end of each sterigma one 

 spore is abjointed (fig. 195'). These basidia, together with a number of slender 

 sac-like tubes, to which reference will again be made when the Basidiomycetes are 

 described in detail, beset certain structures projecting from the under surface of 

 the cap-shaped sporophore — these structures being lamellae or spikes or tubes 



