97 



THE SPROUTING OF THE ZYGOTES. 



The Zygotes now begin to sprout and grow out to long 

 tubes. Fig. 55 PI. IX shows two pollentubes which have 

 entered the enibryosac, the one at the right shows at its tip 

 two zygotes as yet unchanged while the one to the left shows 

 two zygotes which are just beginning to sprout. The sprouting 

 tube may very soon branch (Fig. 50 PL VIII) but as a rule, 

 such branching occurs at a very much later moment. The 

 direction taken by the sprouting zygotes or proembryo's is 

 usually towards the top of the prothallium (fig. 53 PI. IX), 

 and it is seen that the nucleus moves towards the tip of the 

 tube and on arriving there remains. Frequently a small pro- 

 jection is formed at the opposite end of the zygote (tig. 53, 

 55, PI. IX, fig. 60, PL X) and occasionally this projection 

 can become rather long (fig. 51 PL VIII). Usually no septa are 

 formed in these proembryonic tubes but fig. 57, PL X shows 

 one plainly. 



As has allready been said the proembryo's try to reach the 

 top of the prothallium but not unfrequently they get lost on 

 their way. So the proembryo in fig. 5 1 , PL VIII has perforated 

 the wall of the embryosac and penetrated into the nucellar 

 tissue where it will soon perish. Fig. 60 shows a proembryo 

 which has grown in a direction almost diametrically opposite 

 to the right one. 



OTHER CHANGES IN THE FERTIL PART OE THE EMBRYOSAC. 



About the time of the formation of the zygotes it is seen 

 that a greater or smaller number of the nuclei of the fertil 

 part of the embryosac surround themselves with a denser pro- 

 toplasm, a membrane and thus form cells. I will call these 

 retarded prothallium-cells of the fertil part. They may form 

 regularly in the neighbourhood of the young zygotes (fig. 

 44, 45, PL VII) or they may be found rather irregularl}'^ 

 distributed (fig. 60 PL X) or they may be limited to a very 



Ann. Jard. Builenz 2 Ser Vol. I. 7 



