58 FERTILIZATION AND FHUIT-FORMATION IN CRYPTOGAMS. 



If a green filament of Vaucheria is examined under the microscope it is found 

 to consist of a single tube without septa, but with numerous saccate branches. 

 The sac-like outgrowths serve a variety of purposes; those at the base fasten 

 the tube to the substratum, those at the free extremity develop swarmspores, 

 whilst those springing laterally from the filament have the functions of fertilization 

 and fruit-formation. The lateral outgrowths are of two kinds (see figs. 204^ and 

 204^). One form is short, thick, and oval, and usually projects obliquely; the 

 other is a slender cylinder curved like a chamois horn or wound round in a 

 spiral, and sometimes it is subdivided into several little horns. The protoplasm 

 in these sacs severs itself from the protoplasm of the main tube and a partition 

 of cellulose is inserted in the plane of disjunction in each case. We have thus 

 corresponding to each protuberant sac a cell-cavity or receptacle which incloses 

 the protoplasm destined to take part in the formation of fruit. The obliquely- 

 oval receptacles contain ooplasm and are oogonia, the curved, cylindrical receptacles 

 inclose spermatoplasm and are antheridia. Their development is accomplished 

 rather rapidly. It usually commences in the evening, and by the following morning 

 the oogonia and antheridia are already completed. During the course of the fore- 

 noon an aperture appears at the apex of the oogonium, whilst simultaneously the 

 ooplasm within it contracts into a sphere. The spermatoplasm in the antheridia 

 has meanwhile broken up into a large number of oblong spermatozoids, with a 

 cilium at each end. After this has happened the free extremity of the antheridium 

 bursts open, and the minute spermatozoids are expelled in a swarm into the sur- 

 rounding water. Some of them reach a neighbouring oogonium, pass through 

 the opened summit into the interior of the receptacle, and there coalesce with 

 the ooplasm which has contracted into a green sphere. In connection with this 

 phenomenon there is the following very striking circumstance to be noted. 

 Where, as is usually the case, an oogonium and an antheridium are developed 

 in close proximity to one another on the same tube, they seldom open simul- 

 taneously, and this circumstance most efiectively prevents the fertilization of 

 the ooplast by spermatoplasm of the adjacent antheridium; but on the other 

 hand it usually happens that the spermatoplasm from the antheridium of one 

 tube reaches the oogonium of another tube, and in this manner a crossing of 

 the two takes place (figs. 204 ^ and 204 «). 



As soon as an ooplast is fertilized it surrounds itself with a tough cell- 

 membrane; the green colour of the protoplasm changes to a dirty red or brown, 

 and the fruit is to be seen imbedded in the oogonium in the shape of a reddish- 

 brown, unicellular sphere. The oogonium dissolves or else breaks ofi" with the 

 fruit inclosed in it. In either case the product of fertilization is removed from 

 the tube whereon it developed and sinks to the bottom, where it undergoes a 

 comparatively long period of rest often lasting through an entire winter. When 

 the unicellular fruit germinates, the outer layer of the cell-membrane splits, and 

 out of the rent emerges a tube of like form to that which produced the fruit. 



In every case of cryptogamic fertilization hitherto discussed a union of the 



