272 



PLANT LIFE. 



like in form but unlike in l)ehavior. Tliis leads to the com- 

 pletest form of conjugation, as seen 

 in ]\fesncarpus, Spirug^vni, and other 

 Conjugatce. (See *\ 25.) In these 

 the contents of one cell of a filament 

 enter those of another either by a 

 ])arlial solution of the partition-wall 

 between them or by the formation of 

 a tube-like outgrowth from one or 

 fjolh of the cells concerned, so that 

 when these tubes come in contact and 

 have their ends absorbed the contents 

 of one cell passes over into that of 

 the other (fig. 303). The cells con- 

 'C~^ — ■^' G< — 'I jtigating in this way ma)' be either 

 \v-^S±il lr>^^ II "^ neighboring cells of tlie same fila- 

 ment or cells of different filaments 

 brought into proximitv \)\ acccident. 



Fig. 303 —Conjugation of .S>/rff- r i i' ' ■ , ■ 



^,r»-'i ?»/»'■««. The cells 11,1' in the course ot development in tins 



are just forming the conjugat- 

 ing tube ; the contents not yet dirCCtlon conjugation reaches its 

 fully reorganized as gametes. 



The body protoplasm is not hitrl-i,;st perfection, being sccured with 



shown in these two cells, "" 



though it is in the others such ccrtaiiilv that noii-se.vual methods 



(compare fig. 25, of another 



species of .Spn-ogyra). The are aliiiost ciitirelv abandoned. 



cells /', /'' have completed the 



tube ; the ends have been dis- 376. 2. Heterogamy. The seCOud 



solved and the contents of /' 



is passing over into «'. Thispne of de\'elo])ment Was followed by 



process is nearly completed in 



cells c, it', z, z, zygotes, with other algffi, and the method iiro\ed so 



protecting wall, thereby pre- ^ 



pared to become restingspores. efficient that it became the dominant 



Magnified 150 diam. — After 



Strasburger. one in the ]ilant kiugxlom. Among 



these algx there occurred a differentialiou of the zoospores. 

 The first step in this differentiation was an increase iu size 

 of one of the sex cells, so that they differed both in action 

 and in form. To distinguish one from the other the larger 

 sex cell is called the female cell, or egg, and the smaller, the 

 male cell, or sjierm. A fiirther difference arose in the com- 



