204 INTRODUCTION TO CYTOLOGY 



some has elongated to form the blepharoplast, and the nucleus has begun 

 to elongate also. The blepharoplast comes against the apical body at 

 one end of the nucleus; this is to be the anterior end of the spermatozoid. 

 The apical body becomes pointed, while the portion of the blepharoplast 

 lying beside it somehow gives rise to the two long cilia. Meanwhile the 

 limosphere remnant takes up a position near the posterior end of the 

 nucleus where it may eventually disappear along with some of the cyto- 

 plasm. The mature spermatozoid consists of an elongated body repre- 

 senting chiefly the nucleus, a little cytoplasm, an apical body, and a 

 motor apparatus consisting of blepharoplast and cilia. 



It will be noted that the behavior of the limosphere and apical body 

 are almost precisely similar to that of the acroblast and acrosome in 

 animals (p. 220). The acroblast is known to represent the Golgi material 

 of the animal spermatid; hence the demonstration that the limosphere is 

 derived from the plastids of earlier cell generations lends strong support 

 to the view that of all the cell elements in plants the plastids correspond 

 most closely to the Golgi material of animals (see p. 80). 



The spores in bryophytes are borne by the sporophyte, which develops 

 from the fertilized egg. In the sporangium certain cells known as 

 sporocytes round up from one another and each of them undergoes two 

 successive divisions, thus giving rise to a quartet of spores. In some 

 liverworts the sporocyte becomes markedly four lobed before it divides. 

 It is in the course of the two mitoses in the sporocyte that the number of 

 chromosomes is reduced one half. Meanwhile the plastids also are 

 divided (at least in some cases) and distributed to the four spores (p. 70). 

 After their walls become fully developed, the spores are freed from the 

 sporangium and later grow into new gametophytes. 



Pteridophytes. — In pteridophytes, as in bryophytes, quartets of 

 spores with the reduced, or gametic, chromosome number are produced 

 by the division of sporocytes in the sporangium. Furthermore, the 

 spores germinate to produce gametophytes, which bear eggs and sperma- 

 tozoids in archegonia and antheridia. In location and general charac- 

 teristics the egg is much like that of bryophytes. Often it is somewhat 

 flattened on the receptive side at the time of syngamy. 



The spermatozoids of all pteridophytes, except Ly co-podium, Phylloglos- 

 sum, and Selaginella, differ from those of bryophytes in being multiciliate. 

 Most of the accounts of spermatogenesis^ state that the blepharoplasts 

 appear first either in the spermatids or as centrosomes during the divi- 

 sion which differentiates these cells. In Equisetum (Fig. 122) it has 

 been shown that the blepharoplast appears as a functional centrosome 



sfiuchtien (1887), Campbell (1887), Belajeff (1888, 1897, 1898, 1899), Guignard 

 (1889), Schottlander (1893), Shaw (1898a), Thorn (1899), Yamanouchi (19086), 

 R. F. Allen (1911), Sharp (1912, 19146). See the recent studies on the mature 

 spermatozoid by Dracinschi (1930, 1931, 1932) and Yuasa (1932, 1933). 



