CHANGES IN THE 003PHERE. 



435 



more or less protoplasmic 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 synergidoB. The remaining cell is near 

 the lower extremity of the two just de- 

 scribed, and is known as the oosphere. 

 All of these parts are shown in the fig- 

 ures. 



Such, then, is the structure of the em- 

 br3-onal sac and of the egg-apparatus, 

 when the extremit}' of the pollen-tube 

 emerges into the cavitj- of the ovary and 

 comes in contact with the niicrop3-le, or 

 foramen. It has been shown bj"^ Stras- 

 burger, that when contact takes place be- 

 tween the pollen-tube and the summit of 

 the embryonal sac, one of the sj-nergidse 

 changes its character ; its rather clear pro- 

 toplasm becomes turbid, its vacuole and 



nucleus vanish, and with a slight con- 

 traction the mass becomes finelj' granu- 

 lar, after which it ma3- wliollj- disappear. 

 At this time the oosphere 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 confiuent at a later period. The 



Fig. 202. Synergidaj prolonged across the membrane of the embryonal sac. a, 6, c, 

 from Gladiolus communis ; dt from Bartonia aurea. a, plane perpendicular to the 

 plane of the symmetry of the ovule ; b. In the plane of symmetry j c, after separation of 

 the three parts; c2. (Strasburger.) 



Fig- 203. Oapsella Bursa-pastoris. Two embryos with cotyledons distinctly devel- 

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



