1 



DEVELOPMENT OF THE WALLS IN THE PROEMBRYO 



OF PIAWS LARICIO 



CONTRIBUTIONS FROM THE HULL BOL\XICAL LABORATORY 



XCVI 



N. Johanna Kildahl 



(with PLATES VIII AND IX) 

 HISTORICAL SKETCH 



In 1862 HoFMEiSTER (i) gave the principal facts in the develop- 

 ment of the proembryo of Plmis Strobus and Pinus Abies, although 

 he did not touch upon the development of the walls. 



Strasburger (2) worked out the development of the proembryo 

 in more detail in 1876, and he was the first to recognize the arrange- 

 ment in tiers. He says that after the four free nuclei have reached the 

 basal end of the egg, and arranged themselves into a plane, the nuclei 

 opposite each other exert an influence upon the surrounding proto- 

 plasm, giving it a parallel-striped appearance, and that this influence 

 is also exerted upon the protoplasm of the egg mass above the nuclei; 

 a row of granules then appears upon the parallel stripes ; at the meta- 

 phase of the first division, after the nuclei have reached the base of 

 the spore, the stripes and row of granules toward the egg-mass dis- 

 appear, while those between the nuclei persist, form membranes, and 

 become the permanent vertical walls. 



In 1898 Blackman (3), in describing the proembr}^o of Pinus 

 silvestris, said that after the four nuclei have passed to the bottom of 



r 



the egg they become surrounded by protoplasmic fibers which radiate 

 from the nuclei into the cytoplasm; they have no definite arrange- 

 ment, but are mostly directed away from the base of the egg. At a 

 later stage, when the four nuclei have arranged themselves in one 

 plane, the fibers also are confined to the basal end of the egg and form 

 a mass in which the nuclei lie, the mass projecting a little above the 

 nuclei ; after this the two walls are formed at right angles to each other 

 and to the base of the egg, so that each nucleus lies in one end of a 

 shaft which is open toward the main mass of the egg; after the walls 

 have been formed the fibers disappear. He says that he could not 



Botanical Gazette, vol. 44] 



[102 



