﻿1903] BRIEFER ARTICLES 2 1 1 



rospores may become permanent, but in every case where I could be 

 certain, a^ was the nucleus which matured. Zimmerrnann's fuchsin- 

 iodin-green was a very valuable stain for differentiating the reproduc- 

 tive nuclei from the vegetative nuclei, making it possible to distinguish 

 the two with certainty. The cell which becomes permanent is often 

 larger than its sister cells from an early 

 stage; as it enlarges further, their walls 

 break down and their contents are absorbed, 

 leaving the macrospore in a long pointed 

 cavity in the middle of the nucellus. The 

 process resembles that described by Stras- 

 burger (i) in Polygonum divaricatiim. 



The development of the macrospo- 

 rangium in Yucca gloriosa has been worked 

 out by Vesque (2), who described a hypo- 

 dermal cell which gives rise to a two-layered 

 tapetum and three potential macrospores, yio. 3^A young macro- 



but did not follow the development far sporangium at the time of the 



enough to determine which one persisted, formation of the haustorialtube: 



Tl^<^^^ • .- - n .1 I-' t. ^- embrvo-sac mother cell; /, 



Inere is no question, in all the cases which ^' ^^ ^ _ ^ 



T . , , . ,_ .. . placenta. X360. 



filamentos 



stant in having a single layer of tapetal cells and that such cells as 

 a^ and a^, fig, 2, are true macrospores. The fuchsin-iodin-green 

 stain plainly differentiates the nuclei of the different cells. When 

 disintegration begins the three macrospores disappear almost simul- 

 taneously, followed later by the tapetal cells. 



The permanent nucleus now enters upon the divisions which pro- 

 duce the eight nuclei of the embryo sac. Fig. 3 represents the first 

 division and shows the shape of the embryo-sac at that time. The 

 subsequent divisions are accomplished in the lower, pointed end of 

 the cavity. The antipodal nuclei are often separated from each other 

 by distinct cell walls. By the time the sexual nuclei are formed, the 

 tapetal cells and part of the nucellus have disintegrated, leaving the 

 apical end of the embryo-sac in contact with the epidermis of the 



macrosporangium. 



The embryo-sac grows chiefly in the apical part at the expense of 

 the nucellus and tapetum. The basal portion of the sac appears to 

 sink deeper into the nucellus by reason of the elongation of cells in 

 its walls, but it increases in diameter very slightly. The result of this 

 manner of growth is to produce a narrow tube which penetrates the 



