THE MICROSPORANGIUM 35 



diploid plants of Oenothera rubricalyx (Gates and Goodwin, 1930). 

 In the former the tapetal cells are uninucleate and in the latter 

 they are binucleate — a fact which is no doubt related to the general 

 reduction of tissues in haploid individuals. More difficult to ex- 

 plain is the marked difference in shape and structure of the tapetal 

 cells belonging to the same anther. In Lathraea (Gates and Latter, 

 1927), Salvia (Carlson and Stuart, 1936) (Fig. 265), and Moringa 

 (Puri, 1941) the tapetal cells on the inner side of the loculus show a 

 marked radial elongation and are much larger than those on the 

 outer side. Further, in Lathraea the cells on the outer side are uni- 

 nucleate while those adjacent to the connective are binucleate. 

 In Lactuca sativa (Gates and Rees, 1921) the tapetal cells lying on 

 one side of the loculus may be quadrinucleate while those on the 

 other are binucleate. The binucleate cells are nearly always shorter 

 and broader than the quadrinucleate. Possibly these differences 

 are related to the varying amounts of nutritive materials passing 

 into the cells. 



Toward the close of the meiotic divisions in the microspore mother 

 cells, the tapetal cells begin to lose contact with each other. Large 

 vacuoles appear in the cytoplasm and the nuclei begin to show signs 

 of degeneration. 7 Finally the cells are entirely absorbed at the 

 time when the microspores begin to separate from one another. 

 This type of tapetum, in which the cells remain in situ, is called the 

 glandular or secretory tapetum and is of common occurrence in 

 angiosperms. However, there are several genera and families (see 

 Juel, 1915; Tischler, 1915; Mascre, 1919 a, b) in which the walls of 

 the tapetal cells break down but the protoplasts, which remain 

 intact, protrude and "wander" inside the loculus, where they may 

 coalesce to form a continuous mass called the tapetal periplasmodium 

 (Fig. 29). Clausen (1927), who has reviewed the previous literature 

 in this connection, classifies this kind of tapetum (often called the 

 "amoeboid" tapetum) into four subtypes: 



1. Sagittaria type. The tapetal cells lose their walls by the time 

 the microspore tetrads have been formed, and their protoplasts 

 begin to project inward as soon as the microspores have separated. 

 Later the periplasmodium becomes continuous. Examples: Sagit- 

 taria, Alisma, Limnocharis, Hydrocharis. 



7 At this stage the anther loculi frequently show a densely staining jelly-like 

 or mucilaginous fluid which disappears at maturity. As suggested by Nietsch 

 (1941), this is probably a secretion from the tapetal cells. 



