OVULES OF GYMNOSPEKMIA. 



629 



divides and subdivides to form the rosette, which surmounts the 

 central cell. In the upper part of this latter is then formed, from 

 subdivision of the nucleus, a very delicate cell, which is called the 

 canal-cell. The mature corpuscle therefore consists of a large 

 central cell surmounted by a rosette of small cells placed immedi- 

 ately beneath the wall of the primary embryo- sac, or separated 

 from it by a funnel-shaped space. The pollen-tube, after remain- 

 ing passive for a variable space of time, takes on active growth, 

 traverses the endosperm, and arrives at the embryo-sac by the time 

 the corpuscula are developed. It penetrates the wall of the em- 

 bryo-sac, enters into and dilates the funnel-shaped space just 

 mentioned, passes down between the cells of the rosette, pushing 

 them on one side (Taxinece, Cupressinece), or causing their absorp- 

 tion and disappearance (^Abietinece) as well as that of the canal-ceil, 

 and finally penetrates into the cavity of the central cell. The 

 changes which take place in this latter are, according to Stras- 

 burger, these : disappearance of the original nucleus, and forma- 

 tion of four to eight new nuclei by condensation of the protoplasm 

 and subsequent secretion of a cellulose wall around them. In this 



Development of embryo in Coniferae (Pinus) : A, upper part of the embryo-sac, with two 

 corpuscula or archegonia ; B, the same more advanced, the right-hand one with a pollen- 

 tube (p t) in its canal and germinal corpuscles (a) at the base ; C, D, E, successive stages 

 of development of a in B ; F, G-, H, development of these cells into suspensors, at the end 

 of one of which the embryo is produced, shown in I (em)'. Magn. 100 diam. 



way four to eight new cells are formed by free-cell formation in 

 the central cell after fertilization ; these new cells divide so as to 

 form cellular filaments, which break out through the bottom of the 

 endosperm into the substance of the nucleus (fig. 606, F, Gr, H). 

 At the ends of these filaments cell-division again occurs (I) ; and 

 from the apex of one of these suspensors or proenibryos is developed, 

 by repeated cell-division in various directions, the embryo (I, em}. 

 At one stage (in Thuja} a single apical cell, the terminal one of a 



