Connecting Threads in Graft Hybrids. -i 19 
2. Solatium tubingense. In this graft hybrid which has the 
epidermis of the tomato (S. lycopersicum) and the sub-epidermal tissues 
of the black nightshade (S. nigrum), the connecting threads between 
the epidermis and the underlying layer of cells, are demonstrated 
very easily. The material used was taken from the stem of a part 
of the plant which showed the typical hairy tomato epidermis and the 
leaf-shape and other characters of the nightshade. The threads 
connecting the epidermal cells with those of the layer below corres¬ 
pond exactly with those connecting together neighbouring epidermal 
cells or neighbouring cortical cells. The threads are not situated 
in pits though the cell-walls are generally rather thinner in the 
regions perforated by the threads, but the thinning of the wall is 
gradual and not abrupt as in pit formation (see Fig. 1). The median 
node of each thread is very marked and if the cell-wall is split along 
the middle lamella, the median node can often be seen to be split 
also, each half of the fractured thread retaining a dark dot upon 
the broken end. The only difference between the threads con¬ 
necting the epidermis with the sub-epidermal layer, and the threads 
connecting epidermis or cortex inter se is the greater frequency of 
the latter. 
Fig. 1. Solatium tubingense. Transverse section showing connecting threads 
between epidermis (E) and cortex (C). X 1200. 
3. Solatium Kodreuterianum. This graft hybrid is the converse of 
the foregoing, it has the nightshade epidermis and the sub-epidermal 
tissue of the tomato. It was not found possible to demonstrate 
connecting threads in it at all, between any of the tissues. The 
material or methods of preparation must have been unsuitable for 
some reason, though in age and general character the material did 
not seem to differ from that of Solatium tubingense which gave such 
excellent results. 
