Books and Current Literature 



167 



Geological evidence shows the Karroo region to have been 

 desert in Cretaceous time. In the late Tertiary, however, there 

 was a glacial epoch in the southern hemisphere which gave a 

 relatively moist climate to the interior, without depriving the 

 desert flora entirely of favorable localities in which it might sur- 

 vive by northward migration. To the duration of the arid con- 

 ditions, long even in geological terms, Marloth attributes the 

 richness of Karroo and Kaffirland flora as contrasted with the 

 poverty of the more recent Sahara. 



Forrest Shreve. 



A graft hybrid between the tomato and nightshade has been 

 made by Winckler and is reported in the Berichte der deutschen 

 botanischen Gesellschaft, 1908. After showing in some detail 

 that the new plant must be a hybrid, the author considers its 

 probable structural origin, although the actual process by 

 which it arose is not communicated and probably has not been 

 definitely determined. 



It is supposed on theoretical grounds that the cells of the 

 graft hybrid, like the cells of a seed hybrid, must contain chroma- 

 tin which was derived from both the parents. How this con- 

 dition could, in the present instance be brought about is then 

 taken up. The adventitious shoots may have arisen from a sin- 

 gle hybrid cell, or from a cell which had at least nuclei from both 

 parents, as the shoots in Begonia. But the objection to this lies 

 in the observed fact that, in Solanum, shoots do not take their 

 origin from one only, but usually from a mass of cells. 



The interesting possibility is considered that the hybrid may 

 possess nuclei with twice the number of chromosomes found in 

 the parents, which, if found to be a fact, would strengthen, if 

 further proof would seem necessary, the author's contention 

 that the new plant is a true graft hybrid. But it is pointed out 

 that Cytisus Adami, which is supposed to be a graft hybrid, 

 has only the number of chromosomes characteristic of its parents, 

 according to the studies of Strasburger. What the nuclear con- 

 ditions may be in the Solanum hybrid is a matter of great interest 

 and we are promised a report on this phase of the study in due 

 time. 



W- A. Cannon. 



