MEIOSIS 213 



chain of six chromosomes were seen. Another abnormal confi- 

 guration was a ring-pair and twelve chromosomes in a closed chain. 



It will be seen that although the chromosomal constitution 

 of these reciprocal hybrids is the same, yet differences in morpho- 

 logical structure and cytological behaviour is very evident. When 

 CE. amrnophila is the pollen parent, each chromosome of the two 

 groups which are brought together finds a mate, with which it 

 becomes paired. In the case of the reciprocal cross, on the other 

 hand, when what must be regarded as virtually the same chromo- 

 somes are brought together, only six of them pair, the other eight 

 lemaining linked in a ring. It would seem then, that some impor- 

 tant part must be played by the cytoplasm, which is derived from 

 CE. {biennis X ruhricalyx) in one cross and from (E. ammoyhila 

 in the other. When the cytoplasm of the egg is contributed by 

 the constant hybrid CE. {biennis X rubricalyx), 100 per cent, 

 pairing occurs, but when CE. ammophila is the seed parent then 

 eight of the chromosomes remain linked. 



Lathrcea. The rneiotic phase in the pollen mother-cells of two 

 species of Lathrcea {L. clandestina and L. squamaria) has been 

 investigated by Gates and Latter. All five species of this genus 

 are root parasites of different trees and shrubs. It was found 

 that the pollen development in these two species was very similar 

 at all stages and that the haploid number of chromosomes was 

 21 and the diploid 42. This possibly represents the hexaploid 

 condition ; the fundamental number being 7. It was discovered 

 that the method of chromosome reduction does not conform 

 precisely to either telosynapsis or parasynapsis. 



The pollen mother-cells show nuclei with a spherical, deeply- 

 staining nucleolus. The latter contains vacuoles and crystal 

 bodies. The reticulum is granular in appearance, and at the first 

 onset of synapsis this granular appearance of the reticulum is 

 lost and a delicate thread-like structure is revealed in its place. 

 Held in the meshes of the reticulum are dense aggregations of 

 chromatin (Fig. 77, A), the appearance of which is the first indica- 

 tion of approaching synapsis. These homogeneous bodies are not 

 pro-chromosomes, but are definitely parts of the threads them- 

 selves, and are included in the synizetic knot as contraction proceeds. 



