FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAJIS. 69 



i have a spatulate enlargement at one extremity, and carry on the other, attenuated 



I end a regular mane of extremely fine cilia. 



Far more important are the characteristics which distinguish from Ferns the 

 Rhizocarpese and Lycojjodiales, especially the genera Salvinia, Marsilia, and 

 Selaginella, in all of which the development has been studied with great care. 

 The antheridia-bearing prothallia are, in the last-mentioned genera, extremely 

 ditFerent in point of size from those which bear fruit-rudiments. Both prothallia, 

 it is true, have spores for their starting-points, but these spores themselves have 



; different dimensions, and are distinguished as rnicrospores and Triacros'poves {i.e. 



i small spores and large spores). The microspores are the parts of the plant where 

 antheridia are formed, and the macrospores those where fruit-rudiments are formed. 

 In a microspore the protoplasm divides into several parts, and partition-walls are 

 inserted between them, thus forming a tissue composed of a very few cells, the 

 greater part of which remains concealed in the interior of the spore. Only one or 

 two superficial cells of this tissue push out through rents made here and there in 

 the coat of the spore, and these protruded cells constitute the antheridia. The 

 apical cell of the antheridium becomes filled with a tissue, and in each cell of this 

 tissue is formed a spirally-coiled spermatozoid. The opening of the antheridium 

 and the escape of the spermatozoids then ensues in the same manner as in Ferns. 

 The prothallium which originates from a macrospore and is the seat of formation 

 of fruit-rudiments, although it is larger and composed of more cells than that just 

 described, does not forsake the interior of the cavity of the macrospore to any 

 greater extent, but only protrudes a little at one place where the tough outer coat 

 of the macrospore is ruptured. Two kinds of tissue are in reality developed 

 within the limits of each macrospore, viz.: the one above referred to as emerging 

 between the torn edges of the outer spore-coat, and a tissue of reserve material 

 deposited at the bottom of the macrospore. The latter is very rich in starch and 

 oil, and serves as a storehouse of nutriment for the prothallium at least until it ia 

 in a position to get food for itself out of the environment. The fruit-rudiments 

 (amphigonia) appear on the protruding portion of the prothallium, and are entirely 

 buried in its tissue. The development of the fruit-rudiment, the formation of 

 canal-cells which subsequently turn into mucilage, the penetration of the spermato- 

 zoids, and the act of fertilization, are in all essential respects the same as the 

 corresponding processes in Ferns, and therefore a description of them in detail may 

 here be dispensed with. 



The tissue produced from a macrospore in the Rhizocarpese and Selaginelleae has 

 been compared to the ovule as it occurs in the Phanerogams which will be the 

 subject of the next chapter, and certain actual analogies have been brought out 

 which are exhibited by the ooplasm when converted into an embryo, the store- 

 chamber for food-stuffs, and the protective envelope in each case. Having regard 

 to the identity of object aimed at through the instrumentality of these structures in 

 the most widely different sections of the Vegetable Kingdom, such analogies are 

 really a matter of course, and if naturalists limit themselves to proving that organs 



