BULLETIN No. 1.

uc

BRASSICA CROSSES

BY

ARTHUR W. SUTTON, F.L.S., V.M.H.

A Lecture Delivered

Before the Linnean Society,

January 16th, 1908.

PRICE 2s. 6d. Net.

Published by

SUTTON & SONS, READING,

Q Seedsmen By Appointment to His Majesty King George V.

LIBRARY-AGRICULTURE DEPT

!.

NOTES ON SOME WILD FORMS AND SPECIES

OF

TUBER-BEARING SOLANUMS.

By ARTHUR W. SUTTON, F.L.S., V.M.H.

IN 1883, Mr. J. G. Baker, F.R.S., F.L.S., at the suggestion of the late Lord Cath-
cart, made a study of the various species of tuber-bearing Solanums, the results
of which were embodied in a paper presented to the Society on January 17th, 1884.*

Lord Cathcart was interested chiefly in the discovery of some wild species of
tuber-bearing Solanum which could be utilised for crossing with the commonly
cultivated potato, in the hope of obtaining new forms capable of resisting the
attacks of potato-disease fungus, Phytophthora infestans.

It was concluded that Solanum Maglia of Schlechtendahl, generally known
as Darwin's potato, afforded the best prospect of success in the direction, since
this species does not appear to suffer from the disease in its indigenous habitat
in the low-lying swampy soil of the Chonos Archipelago, whereas the ordinary
potato is practically destroyed by the fungus on wet soils in damp seasons.

On August 6th, 1886, I obtained tubers of Solanum Maglia from a plant
growing in the gardens at Kew, the tubers being dug up in the presence of Mr.
Baker and myself.

(Plate 1. Flowers, foliage, &c., of Solanum Maglia, Schlecht., drawn from
living specimens grown at Reading.) — This species, so far as my experience goes,
does not produce fertile seeds when pollinated with its own pollen : although
it blooms very freely, the flowers drop off prematurely. Many hundreds of attempts
were made to fertilize Maglia flowers with the pollen from cultivated potatoes,
but in one instance only was a hybrid seedling obtained, the latter being the
produce of a cross made in July, 1887.

The hybrid, which has been cultivated continuously during the last 20 years,
has smooth tubers nearly white in skin (the tubers of Solanum Maglia are a dull,
dark purple colour), with leaflets more pointed than those of cultivated potatoes.

In addition to experiments with Solanum Maglia, crosses were attempted with
Solanum Jamesii, but from none of these were seedlings obtained.

Resembling Solanum Maglia in its general refusal to set " seed " either when
pollinated with its own pollen or with that from other species, is Solanum
Commersonii of Dunal.

(Plate 2. Solanum Commersonii, Dun., white-flowered form, foliage, flowers,
&c.) — Two forms of this species are known ; one bearing lilac flowers and
corresponding both in this and in all other respects with Dunal's description, and
the other very similar to it but bearing white flowers. In both forms the jessamine-
like scent of the flowers is very noticeable. Of the violet-flowered form I have had
very many tubers collected in a wild state in Uruguay, and Professor Archeavaleta
of Montevideo assures me that there is no other form to be found in a wild state

* See Journ. Linn. Soc., Bot. vol. xx. (1886) pp. 489-507.

2 Wild Forms and Species of Tuber-bearing- Solanums.

in Uruguay. There is, however, reason to think that the white-flowered variety
was introduced into France from Uruguay by a Colonel Robido in the year 1895.
Many attempted pollinations were made with both varieties, but only one weak
seedling from each has been obtained.

In 1901 M. Labergerie, of Verrieres, Vienne, stated that some of the tubers
of Solanum Commersonii (white-flowering type), which had been given him in
the spring of that year by Professor Heckel of Marseilles, had given rise to a new
variety by " sporting " or bud variation. The supposed new plant was named
by M. Labergerie "Solanum Commersonii 'Violet.'' (Plate 3. " Solan >u»
Commersonii ' Violet,' " Labergerie, foliage, flowers, &c.).

Much controversy has arisen in regard to it, since it differs entirely from Solanum
Commersonii in the character of its tuber, foliage, flower, and habit of growth,
as well as in the form and size of its pollen-grains. On account of the very close
resemblance in all its morphological features to the variety of the cultivated potato
known on the Continent as Paulsen's " Blue Giant " (Plate 4. Paulsen's " Blue
Giant " Potato, foliage, flowers, &c.), it has been concluded by most investigators
who have grown the so-called " sport " and the latter variety side by side in the
same soil, that a stray tuber of the " Blue Giant " must have found its way
accidentally into the plantations of Solanum Commersonii in M. Labergerie's
garden.

(Plate 5. Solanum Commersonii, Dun., flowers, tubers, &c. Plate 6.
" Solanum Commersonii ' Violet,' " Labergerie, flowers, tubers, &c. Plate 7.
Paulsen's " Blue Giant " Potato, flowers, tubers, &c.) — On reference to Plate 2
it will be noticed that the seed-berries are distinctly cordiform in shape, much more
so than is seen in any other tuber-bearing Solanum, the usual form of berry in the
wild species being round or slightly oval, and in almost all the cultivated potatoes
distinctly round. The pollen-grains shown on Plate 2 are entirely regular and
elliptical in form. In both these respects true Solanum Commersonii differs greatly
from the " sport " supposed to have been derived from it, as will be seen on reference
to Plate 3.

A comparison between Plates 5 and 6 will show not only the relative form and
size of the tubers in Solanum Commersonii and in the presumed sport, but also
the fact that the tubers of the former (see Plate 5), as in the case of nearly all other
wild species, are borne at the extremity of long underground stolons, whereas the
tubers of the " sport," like all cultivated potatoes, are produced close to the base
of the stem. A further comparison between Plates 3 and 4 will show the complete
similarity which exists between the pollen-grains of the supposed sport and
Paulsen's " Blue Giant," and also between the seed-berries of these two. A
comparison of the hairs on the tips of the petals on Plates 5,6 and 7 is also suggestive.
It will also be seen on comparing Plates 6 and 7 that the tubers of the supposed
sport and Paulsen's " Blue Giant " correspond in all respects.

Besides Solanum Maglia and Solanum Commersonii, I have had the following
wild species under observation and experiment at Reading : —

1. Two distinct forms of Solanum tuberosum sent me by Mr. Stuart, of the
Vermont Experiment Station, U.S.A. One of them, collected in Mexico, Mr.
Stuart considered to be a practically unaltered ancestral form of Solanum tuberosum.

Wild Forms and Species of Tuber-bearing- Solanums. 3

(Plate 8. Solanum tuberosum,, Linn., var.) — The chief points of interest in this
plate are : —

(a) The regular and elliptical form of pollen-grains.

(6) The wheel-shaped corolla, in contrast with the star-shaped corolla of
'Solanum Commersonii (Plate 5). This wheel-shaped corolla is also seen
in Solanum Maglia (Plate 1), in Solanum etuberosum (Plate 9), and almost
universally in the cultivated potatoes.

(c) The round form of the seed-berry, in contrast with the cordiform seed-
berries of Solanum Commersonii (Plate 2).

2. Solanum polyadenium, Greenman, also from Mr. Stuart. This species is one
of the most distinct of all wild tuber-bearing Solanums with which I am acquainted,
the leaves and stems being covered with a dense coat of hairs, and emitting a
strong scent somewhat resembling that of Feverfew, Pyrethrum Parthenium, Sm.

3. Solanum verrucosum, Schlecht. '

4. Solanum tuberosum, var. boreale ( — Solanum Fendleri, A. Gray), from Arizona.
The latter was sent to me by the Rev. J. Aikman Paton, of Castle Kennedy,

Scotland.

5. Solanum etuberosum, Lindley. (Plate 9.)

The five last mentioned wild species, except Solanum etuberosum, flower
freely, and produce fruits containing an abundance of seeds. The plants raised
from seed of these wild species (excepting only Solanum etuberosum} exhibit no
variation whatever from the parents or among themselves, even when the seeds
are taken from plants allowed to flower in close proximity to other species.
Seedlings, however, of the commonly cultivated potatoes differ very widely from
each other, those raised from the seed-berry or fruit generally exhibiting extensive
variation in foliage, colour of tuber, and in habit of growth.

I find that the pollen-grains of all these wild species are of one particular shape,
namely oval or elliptical, whereas the pollen-grains of all the cultivated potatoes
which I have examined are very irregular in form and size, and possibly degenerate.
This fact is clearly illustrated on Plate 12.

One of the forms or species which has proved of great interest, and which on
account of its remarkable exemption from disease may become of economic value,
is Solanum etuberosum, Lindley. This name was given by Lindley in 1834 to a
tuberless Solanum, which he states was obtained from Chile some years previously
by the Horticultural Society. He described it as exceedingly like the ordinary
potato, Solanum tuberosum, Linn., in all its characters, except that it possesses
thickened rhizomes devoid of definite tubers, and the calyx and flower-stalks are
smooth instead of hairy.

It may be remarked here that if Lindley's plant of Solanum etuberosum produced
no tubers, it would have been difficult to propagate it except from seed ; and
judging by the behaviour of the plants I have experimented with, it is not likely
that Lindley's plants reproduced themselves from seed, for two reasons : 1st,
that seed-berries are very rarely formed, and 2nd, when formed the seedlings
resulting therefrom differ so markedly from the parent stock. It may be suggested
that the Solanum etuberosum when growing in the wild state, the tubers, of course,
not being lifted from year to year and replanted, might produce tubers so small

4 Wild Forms and Species of Tuber-bearing- Solanums.

as to be mistaken for " thickened rhizomes devoid of definite tubers," — or that
possibly the plants which Lindley examined may not have been fully developed,
in which case the tubers would not yet have been formed.

The examples of Solanum etuberosum which I possess came originally from
the Botanic Gardens, Edinburgh, in March, 1887, through Mr. Lindsay, and a.i>ain
from the same stock in 1897 from Dr. Bayley Balfour. They produced at first
small tubers about the size of walnuts, and the calyces are hispid ; in other respects
the plants are similar to the type specimen described by Lindley.

Solatium etuberosum has been grown continuously for more than twenty years
in the Trial Grounds at Reading. During that time no variation has occurred
in the characters of the foliage or flowers of the plants. The tubers have also
retained their original form and colour with the exception of an increase in size.

Up to 1906 the plants had never been seen to bear fruits, but in that year a
single berry was found in the centre of the plantation and allowed to ripen.
Whether this was the product of self-fertilization or the result of a cross with
some other Solanum growing near, it is impossible to say.

The seeds taken from this fruit were sown, and during the past season (1907)
twenty young plants were raised. None of these resemble the parent form very
closely, but they exhibit the same variation that is met with among seedlings
of the cultivated potato.

The tubers of the parent Solanum etuberosum are white in the skin and flesh,
and after twenty years of garden culture average about \\ inches in diameter.
Those of the seedlings, however, vary very much in size, some being already as
large as cultivated potatoes : they are also very varied in colour of skin, some
being white, others dark purple, pale blue, or rose-white ; one seedling has given
tubers the flesh of which is deep purple and the skin almost black, characters
which are met with in some of the cultivated varieties now growing in Chile.

The pollen-grains of the parent are elliptical like those of all wild species, and
the seed-berries are round or slightly oval, but are covered somewhat closely
with distinct white spots, in which they differ from the fruits of all other wild
types.

(Plate 10. Solanum etuberosum, Lindl. — White-flowered seedling.) I was

only able to examine the pollen-grains of one of the twenty seedlings above referred
to, and that happened to be a plant bearing white flowers. In this case the pollen-
grains were regular and elliptical, and entirely similar in form to those of the
parent.

N.B. — In order to avoid any doubt as to the parentage of the seedlings above
described, several different blooms of Solanum etuberosum were artificially sclf-
pollinated under controlled conditions in 1907. Ripe fruits were obtained from
several flowers. Seedlings raised from these in 1908 exhibit the same variability
in character of foliage and colour of the flowers as those obtained from the single
berry collected in 1906, the male parent of which was uncertain, and they vary
also in the form and colour of tuber.

Some of the plants raised from the same berry have white flowers, others lilac-
coloured blooms.

Wild Forms and Species of Tuber-bearing1 Solanums.

The pollen-grains of the white-flowered plants of 1908, like the one white-
flowering plant of 1907 already alluded to, are elliptical like those of the lilac-
flowered parent, while those of the lilac-flowered seedling are irregular and polygonal
in form, corresponding closely in these respects with pollen-grains of the cultivated
potatoes. These are illustrated in Plate 12, and on Plate 11 is figured one of the
lilac-flowered seedlings raised by selfing flowers of Solanum etuberosum in 1907,
with drawings of its irregular pollen-grains.

From the uniform character and shape of its pollen-grains, it would appear
that Solanum etuberosum is a primitive specific form, since it agrees in this respect
with admittedly wild species of tuber-bearing Solanums. Moreover, in the great
variability of its seedlings it closely resembles the cultivated potato. These facts,
I think, point to the conclusion that Lindley's Solanum etuberosum may probably
be the parent form of the cultivated potato of to-day.

EXPLANATION OF THE PLATES.

The figures on the Plates were all drawn from specimens growing in the
Reading Trial Grounds.

PLATE 1.
Solanum Mnglia, Schlecht.

A. Inflorescence and upper leaves, £.

B. Flower showing anthers, x 2.

C. Flower showing calyx, x 2.

D. Flower, side view x 2, showing cleft

stigma.

E. Flower section, x 2, showing cleft

stigma.

F, G, H. Cymes with flowers removed, £.
J. Largest leaf on examples examined, J.
K. Pollen, x 300.

PLATE 2.
Solanum Commersonii, Dun.

(White-flowered form.)

A. Inflorescence and upper leaves, large

lower leaf behind, £.

B. Cymes with flowers removed, £.

C. Flower-bud, x 2.

D. Hairs from tips of petals, x 50.

E. Hairs from limb of corolla, x 50.

F. Pollen, x 300.

G. Self-fertilized berries, £
H. Seed, x 2.

J. Cross-fertilized berries,

K. Sections of do., }.

L. Seed, x 2.

PLATE 3.

" Solanum Commersonii ' Violet,' " Labergerie.

A. Inflorescence and upper leaves, large

lower leaf behind, \.

B. Cyme with flowers removed, \.

C. Hairs from tips of petals, x 50.

D. Hairs from limb of corolla, x 50.

E. Pollen, x 300.

F. Berry, £.

G. Section of berry, }.
H. Seed, x 2.

PLATE 4.
Paulson's " Blue Giant " Potato.

A. Inflorescence and upper leaves, large

lower leaf behind, £.

B. Cyme with flowers removed, |.

C. Hairs from tips of petals, x 50.

D. Hairs from limb of corolla, x 50.

E. Pollen, x 300.

F. Berry, \.

G. Section of berry, }.
H. Seed, x 2.

Wild Forms and Species of Tuber-bearing- Solanums.

PLATE 5.
Solanum Commersonii, Dun. (White-flowered form.)

A. Flower from above, showing anthers,

x 2.

B. Flower from below, showing calyx,

x 2.

C. Flower, side view, part of corolla re-

moved, x 2.

D. Flower section, x 2.

E. F, 0. Tubers, J.

H. Stolon cut at + + showing distance
from plant at which tubers are pro-
duced, \.

J. Section of stolon at K. }.

K. Point of section shown at J.

L. External cells of tuber, x 60.

PLATE 6.
" Solanum Commersonii ' Violet,' " Labergerie.

A. Flower from above, showing anthers,

x 2.

B. Flower from below, showing calyx, x 2.

C. Flower, side view, part of corolla re-

moved, x 2.

D. Section of flower, x 2.

E, F, G. Tubers, £.

H. External cells of tuber, x 60.

PLATE 7.
Paulsen's " Blue Giant " Potato.

A. Flower from above, showing anthers,

x 2.

B. Flower from below, showing calyx, x 2.

C. Flower, side view, part of corolla re-

moved, x 2.

D. Section of flower, x 2.

E, F, G. Tubers, J.

H. External cells of tuber: x 60.

PLATE 8.
Solanum tuberosum, Linn., var.

A. Inflorescence and upper leaves,

B. Flower showing anthers, x 2.

C. Flower showing calyx, x 2.

D. Flower, side view, x 2.

E. Flower section, x 2.

F. Pollen, x 300.

G. Cyme with berries, £.

H. Berry, vertical and horizontal sections,

f-
J. Tubers, f

PLATE 9.
Solanum etuberosum, Lindl.

A. Inflorescence and upper leaves with

large lower leaf, £.

B. Flower showing anthers, x 2.

C. Flower showing calyx, x 2.

D. Flower, side view, x 2.

E. Flower section, x 2.

F. Bud, x 2.

G. Bud, x 2.
H. Berry, }.

H1.)

JT, j- White-spotted berries,

J. Berry section. ^.
K. Pollen, x 300.
LL. Tubers, $.

PLATE 10.
Solanum etuberosum, Lindl. (White- flowered Seedling.)

A. Inflorescence and upper leaves, large

lower leaf behind, £.

B. Flower showing anthers, x 2.

C. Flower showing calyx, x 2.

D. Flower, side view, x 2.

E. Flower section, x 2.

F. Cyme, with flowers removed, J.

G. Pollen, x 300.

Wild Forms and Species of Tuber-bearing- Solanums.

PLATE 11.
Solanum etuberosum, Lindl. (Lilac-flowered Seedling.)

A. Inflorescence and upper leaves,

B. Flower showing anthers, x 2.

C. Flower showing calyx, x 2.

D. Flower, side view, x 2.

E. Flower section, x 2.

F, G, H. Cymes with flowers removed,
J. Pollen, x 300.

PLATK 12.
POLLEN OF VARIOUS SPECIES OF Solanum.

A, B, C.

Figures representing the pollen-grains of Solanum verrucosum, Solanum polyadenium,
and Solanum tuberosum respectively, each x 300. Although varying somewhat
in size, the form in each case is regular and elliptical, and is typical of the pollen-
grains of all the wild types I have examined.

D, E, F. Representing the pollen-grains of the cultivated potatoes " Up to Date," " Main-
crop," and " Discovery " respectively, each x 300. There is little if any
difference in the size of these three groups of pollen-grains, and in each case the
form is irregular and polygonal, and thus typical of the pollen of all the cultivated
potatoes I have examined.
Pollen-grains of Solanum etuberosum, x 300.

Pollen-grains of a seedling plant bearing white flowers raised from a berry pro-
duced in 1906. The form of pollen-grains still remains regular and elliptical,
x 300.

Pollen-grains of a seedling plant bearing white flowers raised from a berry pro-
duced in 1907. The form of pollen-grains still remains regular and elliptical,
x 300.

J, K, L.4 Pollen-grains of three seedling plants raised from berries produced in 1907, each
bearing lilac flowers. The form of pollen-grains in each case is irregular and
polygonal, corresponding to that of the cultivated potatoes, x 300.

All pollen-grains shown in I, J, K, and L, were in each case from the flowers artificially selfed
under controlled conditions.

The seedling plants which gave the pollen-grains shown in I and J were raised from the same
seed-berry.

N.B. — The figures of pollen-grains in this Plate, and of those also shown in the preceding
Plates, were drawn when the pollen-grains were dry.

G.
H.

I.

PLATE 1.

SOLANUM MAGLIA, Schlecht.

PLATE 2.

SOLANUM COMMERSONII, Dun. (White-flowered form).

PLATE 3.

"SOLANUM COMMERSONII 'Violet'", Labergerie.

PLATE 4.

PAULSEN'S "BLUE GIANT" POTATO.

PLATE 5.

SOLANUM COMMERSONII, Dun. (White-flowered form).

PLATE 6.

"SOLANUM COMMERSONII 'Violet'", Labergerie.

PLATE 7.

PAULSEN'S "BLUE GIANT" POTATO.

PLATE 8.

SOLANUM TUBEROSUM, Linn., var.

PLATE 9.

SOLANUM ETUBEROSUM, Lindl.

PLATE 10.

SOLANUM ETUBEROSUM, Lindl. (White-flowered Seedling).

PLATE 11.

SOLANUM ETUBEROSUM, Lindl. (Lilac-flowered Seedling).

PLATE 12.

POLLEN OF VARIOUS SPECIES OF SOLANUM.

UNIVERSITY OF CALIFORNIA LIBRARY
BERKFJLEY

Return to desk from which borrowed.
This book is DUE on the last date stamped below.

r
LIBRARY USE

JUL12 1971 1 1

JUN 21967

LD 21-100m-9,'48(B399sl6)476

YD 04789

455749

UNIVERSITY OF CALIFORNIA LIBRARY

W. H. SMITH & So)

Printers,
55 Fetter Lane,
London, EC