DIRECTION OF MOVEMENT OF NUCLEI 229 



the presence in each cell of cytoplasmic and vacuolar contents, 

 the speed with which the invading nuclei advance through the 

 myceUum (in one instance not less than 1 • 5 mm. per hour and 

 probably 2- 0-3-0 mm. per hour) is truly astonishing. 



Direction taken by Nuclei in passing through a Haploid Myce- 

 lium which is becoming Diploidised. — As we have seen, a tiny 

 pin-head mass of hyphal inoculum of the right kind is sufficient 

 to cause the complete diploidisation of a large haploid myceUum 

 3-6 cm. in diameter, at least in so far as the peripheral hyphae of 

 the latter are concerned. 



One may ask this question : when a large haploid mycehum is 

 being diploidised by a small inoculum, do the nuclei derived from the 

 inoculum travel through the large haploid myceUum in directions 

 which are radial and centrifugal in respect to the inoculum so that 

 some of them pass through the older central part of the myceUum, 

 or do the nuclei travel only tangentially around the mycelium, 

 i.e. in a newer and outer zone of the myceUum ? In an endeavour 

 to answer this question a number of experiments were made, of 

 which three will now be recorded. 



Experiment No. 1. A large haploid myceUum (ab), which was 

 5*2 cm. in diameter, was inoculated at its periphery with a minute 

 fragment of a diploid myceUum {AB)-\-{ab), with the result that 

 the large myceUum became diploidised in less than three days. 



A few hours after clamp-connexions had been observed to have 

 developed all around the periphery of the large myceUum, there 

 was removed from that portion of the Petri dish where the myce- 

 lium, was growing a mass of myceUum-covered agar shaped Uke the 

 hub of a wheel with eight spokes, the hub corresponding to the 

 central part of the myceUum and the ends of the spokes to portions 

 of the periphery of the myceUum. The agar so removed was 

 divided up into one central portion (the hub) and eight radial 

 portions (the spokes), and then these nine pieces of agar were set 

 with intervals between them on dung-agar in another large freshly- 

 poured Petri dish (c/. Fig. 130). The mycelium in each of the 

 nine portions of agar removed from the first plate grew out into 

 the fresh dung-agar where it could be readily observed with the 

 microscope. After two days of this renewed growth it was found, 



