200 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



nucleoli), while inside the egg nucleus the male chromatin was still 

 distinguishable from the female. 3 



In most plants gametic fusion takes place when the nuclei are 

 in a resting condition, but there are exceptions. In Lilium Mar- 

 tagon, L. auratum (Welsford, 1914), L. philadelphicum, L. longi- 

 florum (Weniger, 1918), Fritillaria pudica (Sax, 1918), and Viola 

 odorata (Madge, 1929) the fusing nuclei are in prophase. In the 

 cleistogamous flowers of Viola (Madge, 1929) the male nucleus is in 

 a "spireme," and in Malus (Wanscher, 1939) "both gametes are in 

 a spireme stage during their union." In Triticum (Sax, 1918) the 

 first male nucleus and the nucleus of the egg were both found to 

 be in the "spireme" stage, but the second male nucleus had already 

 progressed into the early metaphase stage at the time of its fusion 

 with the polar nuclei. According to some reports, fusion may also 

 take place at a stage even before the male nuclei have recovered 

 from their original telophasic condition. Nawaschin (1909) be- 

 lieved this to be the case in Lilium martagon, Frisendahl (1912) in 

 Myricaria germanica, and Newman (1934) in Acacia baileyana. In 

 Scilla nonscripta, according to Hoare (1934), the male nuclei formed 

 after the division of the generative cell "never pass into a complete 

 resting stage" but show a dense chromatin reticulum which is inter- 

 preted as "the previous early telophase." 



Conflicting statements have been made regarding the presence 

 or absence of a nucleolus in the male nuclei. In certain plants like 

 Cuscula (Finn, 19376) and Camassia (Smith, 1942) no nucleolus has 

 been seen. In Orobanche (Finn and Rudenko, 1930), Crepis (Geras- 

 simova, 1933), Mains (Wanscher, 1939), and Oxybaphus (Cooper, 

 1949) a nucleolus was not distinguishable at the time of formation 

 of the sperm cells but could be seen shortly before or during fertil- 

 ization, and in Taraxacum kok-saghys (Warmke, 1943) it appeared 

 only after fertilization. In Viola riviniana (West, 1930), on the 

 other hand, the male nuclei always showed a distinct nucleolus, and 

 the one entering into triple fusion is said to be represented almost 

 entirely by its nucleolus. In Orchis maculatus (Hagerup, 1944) also, 

 the male nuclei have one or more distinct nucleoli. 



3 In Tacca (Paetow, 1931) and Jussieua (Khan, 1942) syngamy is completed 

 only after 16 to 32 endosperm nuclei have been formed. In Oxybaphus nyctagineus 

 (Cooper, 1949), on the other hand, "nuclear fusion is completed in the zygote prior 

 to that in the endosperm mother cell." 



