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The desert was almost destitute of vegetation; now and then an Ephedra, Oenothera, or bunches of Aristida were seen, and occasionally the level was covered with a growth of Obione canescens, and a low bush with small oval plaited leaves, unknown.
Two cases of sudden mutations have come to my knowledge, producing this same anomaly in allied species. One has been already alluded to; it pertains to the common evening-primrose or Oenothera biennis, and one is a species belonging to another genus of the same family, the great hairy willow-herb or Epilobium hirsutum.
In unbalanced crosses of the genus Oenothera the hybrids of such reciprocal unions are often different, as we have previously shown. Sometimes both resemble the pollen parent more, in other instances the pistil-parent. In varietal crosses no such divergence is as yet known.
The parents were the common evening-primrose or Oenothera biennis and of its small-flowered congener, Oenothera muricata. These two forms were distinguished by Linnaeus as different species, but have been considered by subsequent writers as elementary species or so-called systematic varieties of one species designated with the name of the presumably older type, the O. biennis.
The original number of chromosomes in OEnothera is 14. In the mutation lata this has become 15, and also in another mutation called semilata. The chromosomes before the reduction division are arranged in pairs, each pair consisting, it is believed, of one paternal and one maternal chromosome.
Here were bahia, madia, madaria, burrielia, chrysopsis, corethrogyne, grindelia, etc., growing in close social congregations of various shades of yellow, blending finely with the purples of clarkia, orthocarpus, and oenothera, whose delicate petals were drinking the vital sunbeams without giving back any sparkling glow.
We recognize the parental marks more or less clearly, but are not prepared for exact delimitations. Leaving these theoretical considerations, we will pass to the description of some illustrative examples. In the first place I will describe a hybrid between two species of Oenothera, which I made some years ago.
These table-lands were always barren, and covered with the same thin gray vegetation, but sometimes adorned with a few flowers the beautiful agemone or prickly poppy, with its blue-green leaves, large white petals and crown of golden stamens; the pretty fragrant abronia, and the white oenothera.
It is to be noted here, a fact emphasised by DeVries in his earliest publications on the subject, that in nearly all, if not all cases, a mutation does not consist in a peculiarity of a single organ, but in an alteration of the whole plant in every part. In this respect mutations as observed in Oenothera seem to be in striking contrast to the majority of Mendelian characters.
I have crossed another elementary species, the Oenothera hirtella with some of my new and with some older Linnean species, and got several constant hybrid races. Among these the offspring of a cross between muricata and hirtella is still in cultivation. The cross was made in the summer of 1897 and last year I grew the fourth generation of the hybrids.
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