FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 67 



all of which are classed together under the name of Vascular Cryptogams, on account 

 of the presence of vascular bundles in their stem -structures and phylloclades. 

 The first generation of these Vascular Cryptogams, whereon are developed the 

 antheridia and fruit-rudiments, also resembles in an unmistakable manner the first 

 generation in certain Liverworts. 



In Ferns, which constitute the most extensive section of the Vascular Crypto- 

 gams, and may be taken as their type, the first generation makes its appearance in 

 the form of a flat, green, foliaceous structure, usually reniform or heart-shaped, 

 lying in close contact with the nutrient soil (see fig. 189 ^^). Inasmuch as the tissue 

 of this first generation nowhere contains vascular bundles, it must be looked upon as 

 a thallus, and has received the name of prothallium. The Fern-prothallium bears the 

 fruit-rudiments as well as the antheridia upon its under surface, which is in contact 

 with the nutrient soil, and which adheres to it by means of a number of delicate 

 hair-like suction-cells. Some Ferns develop the fruit-rudiments and antheridia on 

 separate prothallia; others produce them both on the same prothallium. In the 

 latter case the fruit-rudiments are situated near the sinus of the prothallium, and 

 the antheridia on the part remote from the sinus. Each fruit-rudiment may be 

 compared to a flask in shape, and arises from a superficial cell of the prothallium 

 which is only slightly arched outwards. This cell is divided by the insertion of 

 two partition-walls into three cells, each of which is again segmented in definite 

 directions. From the uppermost cell is produced a tissue which forms the neck of 

 the flask-shaped fruit-rudiment; the middle cell gives rise to three cells, of which 

 the two upper, the canal-cells, occupy the neck, whilst the undermost one becomes 

 the relatively large and subsequently rounded ooplast. The daughter-cells de- 

 veloped from the lowest primary cell take the form of an investing wall round the 

 ooplast, or, to return to the analogy of a flask, constitute the wall of the ventrally 

 enlarged portion of the flask. The protoplasm of the ooplast is the ooplasm, and 

 is now to be seen surrounded by a pluricellular tissue, which, as in the case of 

 Characege and Muscinese, may be called an amphigonium. Only the neck of the 

 amphigonium projects above the other adjacent tissues of the prothallium; the 

 enlarged ventral portion is, as it were, sunk in the substance of the prothallium. 



The antheridia are also developed from cells upon the surface of the pro- 

 thallium. These cells project in the form of papillae above the surrounding tissue 

 and undergo division by the introduction of partition-walls. The outermost 

 daughter-cell becomes enlarged and assumes a globular shape, and from the proto- 

 plasm in its interior are formed spiral spermatozoids. Another mode of origin 

 consists in the formation of a papilliform or hemispherical protuberance of tissue 

 which shows unmistakably a differentiation into central cells destitute of chloro- 

 phyll and enveloping cells containing chlorophyll. The former divide up and a 

 filling-in tissue is formed, the small constituent cells of which contain spermato- 

 plasm. After the development of a spermatozoid in each of these small cells, the 

 whole of the filling-in tissue falls to pieces, that is to say, the individual cells 

 separate from one another and remain for a short time disconnected but still in 



