50 



FERTILIZATION AND B^RUIT-FORMATION IN CRYPTOGAMS. 



sufficient to remark in order to explain the illustration that the attached unicellular 

 fruit does not produce again immediately a string of cells, but that first of all 

 swarmspores are developed from its protoplasm (see figs. 201'' and 201^^), and these 

 fasten on to appropriate spots, inclose themselves in cell membranes, divide and ulti- 

 mately initiate new filaments composed of cells arranged in linear series as before. 



In Ulothrix and allied genera the protoplasts which pair as a first step to the 

 formation of fruit do not differ from one another in form, size, colour, or mode of 

 locomotion, and it would be impossible to determine from outward appearances 

 which of them acts as fertilizer and which is fertilized. The terms ooiilast and 



Fig. 201.— Fertilization and fruit-formation in Ulothrix zonata (partly after Dodel-Port). 



1 Two filaments composed of cells joined together in chains. - Escape of conglomerated gametes. 3 Spherical conglomerate 

 of gametes after it has escaped. * Separation of the gametes. = Gametes swimming about and pairing. 6 Fruits (products 

 of the pairing of gametes) attached to a substratum, f-9 Subsequent development of fruit, lo Two swarmspores produced 

 by fruit, i x 250; 2-io x 400. 



spermatoplast are therefore not applied to them, but they are called gametes, and 

 the entire process described in connection with them may be spoken of as fruit- 

 formation hy pairing of gam^etes. This process of pairing is, so far as it can be 

 apprehended by our senses, a mutual permeation of the two protoplasmic bodies, 

 and we may suppose that a rearrangement of molecules is caused thereby, which 

 endows the product of pairing with the power of developing independently. This 

 assumption is supported in particular by the fact that if any gametes, after being 

 set free from the conglomerate, fail to pair they undergo no subsequent develop- 

 ment but deliquesce in the surrounding water and perish. 



The Wracks or Fucacese, which grow profusely in the sea, resemble Ulothrix 

 inasmuch as the protoplasts, destined to act as fertilizers, escape from their cell- 

 cavities, fertilization consisting of a fusion of free protoplasts disconnected from the 

 mother-plant. But these Wracks diflfer very strikingly from ulothrix and allied 

 forms in that the protoplasts are of two kinds, there being an obvious diversity in 



