PLASTIDS 



71 



ium, also, the plastid shows a plastosome substance and a plastonema in 

 the form of a network or series of plates. In the androcyte (spermatid), 

 or cell which is to become a spermatozoid, the plastid becomes a large 

 limosphere; this buds off a small portion which becomes an apical body 

 at the anterior end of the spermatozoid (see Chapter XIV). In the 

 sporocyte of Catherincea undulata the large plastid is said to be formed 

 by the aggregation of several small ones present in earlier stages 

 (Senjaninova). The plastid lying in each spore divides to several, each 

 of which consists of a series of plate-like elements and clearer regions 

 containing starch. ^^ 



In such cases as those just described the plastids in the spores divide 

 and develop into those of the ensuing gametophyte generation. These in 

 turn give rise to the plastids of the egg, in which, as a rule, they seem to be 



Fig. 34. — Behavior of plastids during sporogenesis in Polytrichum commune, a, 

 division of plastid being completed in archesporial cell, h, reticulate stage of plastids in 

 lobed sporocyte. c, quartet nuclei formed; each cell after cytokinesis will contain one 

 plastid. d, young spore with two plastids formed by division. {After Weier, 1931a.) 



reduced to primordia or small leucoplasts. The spermatozoid carries a 

 plastid product (apical body) but apparently no true plastid; hence the 

 plastidome of the sporophyte is derived from that of the egg. 



Our knowledge of parallel phenomena in vascular plants is rather 

 meager. In Ginkgo each microspore receives about one-fourth of the 

 plastids of the sporocyte (Mann, 1924). A number of investigators^^ 

 have described a more or less equal distribution of numerous small 

 bodies to the four spores as the sporocyte divides. Although these 

 bodies have been referred to wholly or in part as chondriosomes, it is 

 obvious that at least some of them are plastids or their primordia. Very 

 little is known about plastids in angiosperm gametes. Guilliermond 

 (1924) figures small plastids or chrondriosomes in the egg of Lilium. 

 Ruhland and Wetzel (1924) find that the chloroplasts gradually lose their 

 color and come to resemble chondriosomes in the generative cell in the 

 pollen tube of Lupinus luteus, but their behavior in the uniting gametes 



" In this and several other works in this field the minute bodies developing into 

 or arising from plastids are referred to as "chondriosomes," and the thready or plate- 

 like elements of the plastid are regarded as "chondriosomal" in nature. This involves 

 a puzzling question discussed in Chap. VI. 



" Nicolosi-Roncati (1910), W6ycicki (1912), Wagner (1915), Guilliermond 

 (1920e, 1924), Suessenguth (1921), Devise (1922), Lewitsky (1925), Senjaninova 

 (1927c), Py (1929). See the review by Wagner (1927a). 



