60 FERTILIZATION AND FRUIT- FORMATION IN CRYPTOGAMS. 



stalk-like cell, and below the stalk fresh tubular outgrowths develop from the 

 hyphal filament in question which become septate and ultimately form a voluminous 

 multicellular envelope round the embryo. 



The now mature fruit preserves its connection with the parent-hypha, and is to 

 be seen seated upon it in the form of a minute sphere. When a large number of 

 fruits are developed simultaneously on the hyphal reticulum— as is the case in 

 Sphcerotheca Castagnei, which is parasitic on the leaves of Hops— the grey mildew 

 spread over the foliage has the appearance of being studded with the tiny globular 

 heads. From the embryo a new generation is produced. In the species of the 

 genus Podosphcera it develops, within the cellular mass just referred to as investing 

 the fruit, into a single tube (ascus). The protoplasm within the ascus breaks up 

 and fashions itself into true spores, which abandon the tube and are distributed by 

 the wind. In Erysiphe, on the other hand, the embryo becomes septate, and takes 

 the form of a simple or branched chain of cells, and it is not till after this stage 

 that tubes are produced whose protoplasm is transformed into a group of spores. 

 The tubes in question are long, erect, and club-shaped, and they spring from the 

 cells of the aforesaid chain. 



The manner of fertilization and fruit-formation in PeniciUiuvn, and generally 

 in all the forms of Mould which are comprised under the name Aspergillese, is the 

 same as that described in the case of Mildews (Erysiphese). In them also the 

 extremities of tubular hyphse which contain the ooplasm and spermatoplasm, 

 respectively, come into close contact. They are either spirally twisted and wound 

 round one another, or else the extremity corresponding to an antheridium is hooked 

 and grasps the other, as is shown in fig. 193^ (p. 18). Fertilization takes place 

 by osmosis. The embryo produced by the spiral oogonium is septate and multi- 

 cellular, and develops club-shaped or egg-shaped outgrowths, whose protoplasm 

 breaks up into round or ellipsoidal balls (fig. 193 '^). This structure becomes 

 surrounded by a continuous multicellular tissue, which owes its origin to the 

 upgrowth of a number of hyphse from the cells at the base of the oogonium. 

 These hyphse elongate rapidly, ramify, become intertwined, and develop septa until 

 they constitute a spherical envelope round the embryo. The fruit thus constructed 

 is in Penicillium about half a millimetre in diameter. 



The Floridese, or Red Seaweeds, are likewise fertilized by means of osmosis. The 

 details of the process are, however, intrinsically different from those observed in 

 Mildews and in the Moulds classed as Aspergillese. The organs developed for the 

 purpose of fertilization have also quite a different form in Florideee. Their most 

 striking feature is the so-called "trichogyne", a long filamentous cell which projects 

 far above the fruit-rudiment. From this structure the characteristic mode of 

 fertilization in Floridese is called fertilization by aid of a trichogyne. In some 

 Floridese the cell containing the ooplasm leads directly into the trichogyne; in 

 others the fruit-rudiment which incloses the ooplasm is septate, that is to say, it 

 consists of a row of broad cells which together form a short branch of the 

 ramifying thallus, and adnate to one side of this row of cells is the long, delicate, 



