All of the plants on Wizard Island are common on the adjacent mainland, the nearest approach being on the west at Skell Channel, a distance of only 350 yards. This is really a very short barrier for the transportation of seeds and spores. Any of these could have been floated across the narrow channel in the fresh water without injury, or even across other and much longer passages; or plants themselves, cast into the water by slides and other means, could have been included. Seeds provided with special means for flying could easily have been carried by winds; while yet others were doubtless conveyed by birds, driftwood, and other means. Without doubt many seeds and plants reaching the island were unable to establish themselves because of the adverse conditions there. Many, especially shallower rooted forms, could not have maintained themselves after germination, especially during the earlier stages of rock disintegration and soil formation. In this connection it is interesting to note that a very considerable number of plants of common occurrence within that part of the Crater wall nearest to the island have not as yet made their way across the narrow water barrier. It would seem likely that most of these will in time reach the island and become established.

Approximately two-thirds of the species on the island are trees, shrubs, and perennials. The remainder is made up largely of biennials, with only a few more shallow rooted forms growing in situations having less unfavorable soil and moisture conditions. Nearly all of the 60 odd species are provided with highly developed root systems. These serve the double purpose of safe anchorage in the commonly loose, sliding material in which they grow, and of making provision for reaching moisture. At the same time they act as excellent soil binders, helping to make more suitable conditions for the introduction of other species as time goes on.

The zonal distribution is essentially Hudsonian, more than half of the species being truly characteristic of that zone, while most of the others are usually found within it.

Of the six trees (all conifers), the Western Hemlock (Tsuga mertensiana (Bong.) Sargent) predominates on the lower half of the island while the timberline White Bark Pine (Pinus albicaulis Engelm.) has the same predominance at the summit of the cone, where it characteristically encircles the crested rim of the Wizard crater. Within the crater, and especially at its bottom, where soil and moisture conditions are of the most favorable for their growth and maintenance, are to be found some of the more shallow rooted forms, such as grasses, sedges, rushes and Tolmie's Saxifrage (Saxifraga tolmiei T. & G.).

While a considerable proportion of the species are more or less generally distributed, certain ones occur in greater abundance either on the exposed, steeper slopes toward the summit, or within the less precipitous areas about the base. It would seem that the distribution is not so much due to altitude as to such local factors as slope, exposure, soil, and moisture.

Among the plants peculiar or in greatest abundance in the lower areas might be mentioned: Western Hemlock (Tsgua mertensiana (Bong.) Sargent), Shasta Fir (Abies magnifica shastensis Lemmon), Lodge-pole Pine (Pinus contorta murrayana (Balf.) Engelm.), Western White Pine (Pinus monticola Dougl.), Alpine Fir (Abies lasiocarpa (Hook.) Nutt.), - all conifers, named in order of frequency - Lace Fern (Cryptogramma acrostichoides R. Br.), Bleeding Heart (Dicentra formosa Andr.), Mountain Ash (Sorbus sitchensis Roem.), Red-fruited Elder (Sambucus racemosa callicarpa (Greene) Jepson), Crater Lake Currant (Ribes erythrocarpum Coville), White-veined Wintergreen (Pyrola picta Smith), One-sided Wintergreen (Pyrola secunda L), Stick Candy (Allotropa virgata T. & G.), Chamisso's Arnica (Arnica chamissonis Less.), Hart-leaved Arnica (Arnica cordifolia Hook.), Parrot Peak (Pendicularis racemosa Dougl.), Fire Weed (Epilobium angustifolium L.).

Included in the upper areas named the more common are: White Bark Pine (Pinus albicaulis Engel.), Mountain Ocean Spray (Holodiscus discolor glabrascens Greenman), Wooly-leaved Erioganum (Erioganum pyrolaefolium coryphaeum T. & G.), Western Wind Flower (Anemone occidentalis Wats.), Martendale's Cogswellia (Cogswellia martindalei Coult. & Rose), Crater Lake Sandwort (Arenaria pumicola Coville), Applegate's Paint Brush (Castilleja applegatei Fernald), Spider-web Paint Brush (Castilleja pilosa arachnoideus Greenman), Mountain Daily (Hulsia nana Greene), Silver Plant (Raillardella argentea Greene), Brewer's Sedge (Carex breweri Boott.), Parry's Rush (Juncus parryi Engelm.), Tolmie's Saxifrage (Saxifraga tolmiei T. & G.), and Lace Fern (Cheilanthes gracillima Eaton).

It is interesting to note that the following plants occur within the wall of the Crater adjacent to Wizard Island. The plants do not occur on the Island so apparently the seeds of these have not been able to negotiate the 350 yard water barrier, or else have found the soil conditions unfavorable for establishment.

Dwarf Maple (Acer glabrum Torr.), Millfoil (Achillea millifolium lanulosa Piper), Thin-leaved Alder (Alnus tenuifolia Nutt.), Service Berry (Amelanchier florida Lindl.), Long-leaved Arnica (Arnica longifolia D. C. Eaton), Squaw Carpet (Ceanothus prostratus Benth.), Live-for-ever (Cotyledon oregonensis Wats.), Scarlet Bugler (Gilia aggregata Willd.), Dwarf Juniper (Juniperus sibirica Burgsd.), Stickseed (Lappula diffusa (Lehm) Greene), Brewer's Mitre-Wort (Mitella breweri Gray), Daggerpod (Parrya menziesii (Hook.) Greene), Heather (Phyllodoce empetriformis (Smith) D. Don), Jacob's Ladder (Polemonium humile Roem & Schultz), Shasta Smartweed (Polygonum shastense Brewer), Sticky Currant (Ribes ciscessimum Pursh), Creeping Raspberry (Rubus lasiococcus Dougl.), Eastwood's Willow (Salix eastwoodiae Cockerell), Mountain Ash (Sorbus sitchensis Roem), Solomon's Seal (Smilacena amplexicaulis Nutt.), Greene False Hellebore (Veratrum viride Ait), Mountain Violet (Viola purpurea Kell.).