December 17, 190HJ 



NATURE 



205 



tlie same as at the other islands, but is more changed, 

 and possibly contains some mineral other than calcium. 

 The most interesting feature was the presence of big pits, 

 some verv deep, all over the island. The rock seems to 

 be honeycombed with holes, sometimes covered in and 

 sometimes open through the falling in of the superficial 

 layer. Further, in three of these pits I found mangroves 

 growing, all of very great age. Two contain Brugiera 

 and one Ceriops. 1 thoroughly explored all these holes, 

 digging where possible. In one mangrove hole the bottom 

 was guano ; I dug iS inches, but water came in so quickly 

 that we could go no further. The water was salt. The 

 crowbar showed at least 5 feet more " guano mud." The 

 hole was about 8 feet deep, and so there must have been 

 at least 13 feet altogether. There was plenty of man- 

 grove (Brugiera) seed, but very few young trees. This 

 hole was on the eastward side of the island, near the sea. 

 In another hole, just west of the centre of the island, the 

 trees were also Brugiera. This hole was very deep (25 feet 

 to 30 feet.l, with pools of brackish w-ater (undoubtedly from 

 the sea). Digging again was hopeless, and the crowbar 

 found no bottom. I found some shells in the mangroves, 

 most of which were dead. In another hole (north of the 

 island) there were Ceriops trees. The hole was 12 feet 

 deep, the bottom wet and muddy, salt w'aler standing on 

 one side (and fluctuating with the tide). We tried digging 

 here with more success, the water coming in from the 

 sides, and not the bottom. We got down two holes 15 feet, 

 and then found a great lump of coral, which the 

 crowbar broke off. The water got so high that I 

 could not tell whether this was a coral lump tumbled 

 off the walls and fallen by chance in a natural position, or 

 whether it was the bottom of the hole. So I dug another 

 hole, and at a depth of 6 feet came to a soft, white 

 ooze rock ; how much of it there was I do not know, as 

 we could only grovel for bits broken off by the crowbar 

 in 4 feet of mud and water. How the mangroves got into 

 these pits I cannot imagine. There is certainly nothing 

 more than a free percolation from the sea. The only 

 suggestion I have is that there have been two elevations, 

 and that after the first the island was only a foot or two 

 out of the water, possibly with protecting sand round the 

 edge, and that it was covered with mangroves. 



In one hole I found the remains of land tortoises, which 

 arc certainly extinct now. Is there any historical 

 evidence?" I send all I could find to try and ascertain 

 the species, or rather to see if it is the same as the 

 Aldabra one. I also send some things found by the 

 manager in the guano which look like eggs of these 

 tortoises. I heard that the same had been found also at 

 Cosmoledo. 



The deepest hole was 45 feet deep, and contained 23 feet 

 of water, which in all cases was salt. I tried to think 

 if a lagoon formation could take place this way, but do 

 not quite see it yet. The holes are certainly increasing 

 in size owing to erosion and weathering, but must at the 

 same time get shallower. There are some high dunes, 

 70 feet, at the south-east ; wherever there is sand on the 

 east of an island a dune is formed ; as a rule, however, 

 this side is bare rock, as the sea is very heavy, and keeps 

 it clear of sand. 



The vegetation of .Assumption differs slightly from that 

 of the other islands in that there are numbers of tanghain 

 (Euphorbia aibotti) and la fouche (Ficus) trees, which give 

 the land a different appearance. Of animals, I caught twc 

 species of bat, from which I got some Nvcterobia. 



J. C. F. Fryer. 



THE ORIGIX OF THE POTATO. 



T r is a curious fact that the origin of the potato of 

 ■*• commerce, Solarium iuherosuin, that is, the wild 

 species from whence it was derived by selective cultivation, 

 has hitherto baffled research, none of the many wild 

 species of that genus agreeing sufficiently closely in 

 character to be identified with any of the innumerable 

 varieties existing. This in itself might have been of little 



I No.— J. S. G. 



NO. 2042, VOL. 79] 



importance had not the outbreak of the potato disease 

 in the last century suggested the wisdom of finding the 

 original wild species, and by crossing it with the cultivated 

 forms, of infusing fresh vigour into the latter, and thus 

 to some extent fortifv Ihem against that destructive 

 plague. To this end '.Mr. A. W. Sutton, of Reading, 

 collected as many of the wild species as he could from 

 the native habitats in Chili and Peru, and also from out- 

 side sources in North America and elsewhere, but none 

 of these could be accepted as the parental form of the 

 potato of commerce, and though many experiments were 

 made in the way of hybridisation, the results were entirely 

 negative so far as obtaining an improved strain was con- 

 cerned, and the trials consequently ceased. 



A fresh impulse was given to Mr. Sutton's researches by 

 the alleged appearance in France of a " sport " from a 

 wild species known as Solanum commersoiiii, which 

 " sport " was declared to be fully equal to good varieties 

 of the potato of commerce, though it had arisen, as the 

 presumed raiser asserted, from a tuber of the wild species 

 named. Not only, however, did this " sport " resemble 

 closely a cultivated potato in all its characters, but investi- 

 gation proved to all practical potato growers and experts 

 that it was identical with a well-known variety, and that, 

 in point of fact, it must have originated from a tuber 

 or part of a tuber of that variety which had accidentally 

 been in the soil in association with the wild tubers. The 

 renewed research to establish this fact had, however, the 

 result of re-directing Mr. Sutton's attention to another 

 wild species called S. ctuberosum, which had been grown 

 in Mr. Sutton's ground for some twenty years, but which 

 until 1906 had not been observed to produce any seed- 

 berries, and had consequently not lent itself to semina 

 culture, but during that period its tubers, originally small 

 and about the size of marbles, but white and edible, had 

 increased to 2 inches to 3 inches in diameter, and when 

 cooked resembled closelv an ordinary potato. In igob. 

 however, one seedberrv was observed, and the opportunity 

 of sowing was immediatelv seized upon. Hitherto all the 

 recognised wild species when sown yielded true offspring, 

 that is no variation at all was observed, and Mr. button s 

 surprise mav therefore be judged when the twenty plants 

 produced from this seedberrv were not only of very v-aried 

 character in foliage, flowers, and tubers, these last being 

 of many colours and shapes, but they were diverse on 

 preciselv the lines of a batch of seedlings of the common 

 potato 'from which, indeed, they could not be discriminated 

 even bv an expert. The idea consequently arose that this 

 might be due to cross-fertilisation with one of the ordinary 

 potatoes in the vicinitv, and though Mr. Sutton s experi- 

 ence led him to doubt this, he proceeded to check these 

 results bv a second sowing in 1908 from several seed- 

 berries which had been successfully self-fertilised by hand 

 and were consequents free from suspicion. Ihe resulting, 

 plants, however, were equally diverse, and on the same 

 lines A second suggestion was then made that the parent 

 plant, S. ctuberosum, was not really a wild species, but 

 an escape from cultivation; but here, apart from the 

 orio-inal smallness of the tubers, the botanist steps in, lor 

 all the wild species examined have pollen grains ot a 

 svmmetricallv oval or elliptical shape, and S. etubcrosum 

 has them of' same form, while all pollen grains examined 

 of cultivated potatoes are extremely irregular m ^'^^ ana 

 shape, ahd no true elliptical ones are seen. Ihe true 

 specific character of 5. eU.berosum is thus established, 

 while the identity of its offspring with that of the com- 

 mercial potato equally establishes the fact of its being 

 the original wild species. 



Finally a most important economical fact remains to 

 be mentioned. For more than twenty years S. etuberosum 

 has entirely defied the potato disease in the Reading 

 grounds, though year after year subjected to infection by 

 closely adiacent plants. The result originally aimed at 

 w^hen the experiments commenced is thus more _than 

 achieved, since there is no necessity for cross-fertilismg 

 with the ordinary potato, which is susceptible to disease, 

 and consequently' we have all the vigour of the wild type 

 without any tai'nt whatever in the new strain of disease- 

 proof or disease-resisting potatoes which, it is hoped, has 

 ' now appeared. Chas. T. Druerv. 



