CHANGES IN THE OOSPHERE. 



435 



more or less pi'otoplasmic matter, but are not invested by a 

 true cell-wall ; these have been termed the 

 egg-apparatus. Two of these naked nu- 

 cleated bodies are somewhat attenuated at 

 their upper part and rounded below ; the 

 slender portion contains the nucleus, the 

 rounded a vacuole. The bodies are termed 

 the synergidce. The remaining cell is near 

 the lower extremity of the two just de- 

 scribed, and is known as the odsphere. 

 All of these parts are shown in the fig- 

 ures. 



Such, then, is the structure of the em- 

 bryonal sac and of the egg-apparatus, 

 when the extremity of the pollen-tube 

 emerges into the cavity of the ovar} 7 and 

 comes in contact with the micropj'le, or 

 foramen. It has been shown by Stras- 

 burger, that when contact takes place be- 

 tween the pollen-tube and the summit of 

 the embryonal sac, one of the synergidae 

 changes its character ; its rather clear pro- 

 toplasm becomes turbid, its vacuole and 



nucleus vanish, and with a slight con- 

 traction the mass becomes finely granu- 

 lar, after which it rna\- wholly disappear. 

 At this time the ob'sphere also undergoes 

 the following changes : it clothes itself 

 with a thin film of cellulose, and in its 

 protoplasmic mass a well-marked nucleus, 

 probably derived as such from the pollen- 

 tube, appears by the side of the nucleus 

 of the oosphere, sometimes of the same 

 size, sometimes smaller. The two nuclei 

 blend, forming a single ovoid body, with 

 distinct or with confluent nucleoli. Even 

 if at first distinct the nucleoli may be- 

 come confluent at a later period. The 



FIG. 202. Synergidse prolonged across the membrane of the embryonal sac. a, b, c, 

 from Gladiolus cominunis ; d, from Bartonia aurea. a, plane perpendicular to the 

 plane of the symmetry of the ovule ; b, in the plane of symmetry ; c, after separation of 

 the three parts ; d. (Strasburger.) 



FIG. 203. Capsella Bursa-pastoris. Two embryos with cotyledons distinctly devel- 

 oped. B more advanced than A. (Luerssen.) 



