3o8 CHROMOSOMES IN HEREDITY : PHYSIOLOGICAL 



mitosis, the prophase in salivary glands shows the heterochromatin 

 understained or unrecognisable ; the difference is there, but it is 

 reversed (Ch. XI). An analogous reversal we shall see elsewhere. 



(B) Secondly, there is a uniform " precocity " shown in some 

 organisms by all the chromosomes in their proximal parts at the 

 pachytene and diplotene stages of meiosis. This over-condensation 

 on both sides of the centromere was first seen in Agapanthus (Belling, 



V .^^ 



Fig. ioo. — Mitotic nuclei of Sphcsrocarpos texanus [n = y -{- X). 

 Above, resting nuclei with and without a condensed X chromo- 

 some. Below, successive stages of prophase showing the 

 precocity of the X. X 3000 (Tinney, i935)- 



1928 ; Geitler, 1933 ; D., 1933). It has so far been found only in 

 plants, e.g., in Zea Mays (D., 1934) with aceto-carmine treatment, 

 and in (Enothera (Catcheside, 1931) and Canna (Offerijns, 1935) at 

 diplotene. In Fritillaria, where it is accentuated by re- staining, it 

 is associated with earlier pairing and earlier diplotene separation 

 of the condensed part (D., 1935). It is not known to be correlated 

 with different behaviour at other stages of the life cycle, except 

 the meiotic interphase, and in Pellia it is clearly unrelated with the 

 mitotic differentiation (Jachimsky, 1935). It can, therefore, be 



