OCR Text |
Show 180 HETEROSrrYLED rrRIMORPHIU PLANTS. CHAP. IV. the pollen-grains from the two sets of anthers do not differ in diameter. . .. S facts communicated to me by Fntz Muller orne ·r f afford excellent evidence of the ~tter st_en Ity o o~e f tl forms of certain triinorphic species of Oxahs, 0 10 . s c h . when growing isolated. He has seen In t. at anna, in Brazil, a large field of young sugar-cane, many acres in extent, covered with the red blossoms of one fonn alone, and these did ·not produce a single seeu. His own land is covered with the short-st~le~ form of a white-flowered triinorphic species, and this Is equally sterile; ·but when the three forms were plante.d near together in his garden they seeded free_ly. 'Yith two other trimorphic species he finds that Isolated plants are always sterile. . Fritz Muller fonnerly believed that a speCies of Oxalis which is so abundant in St. Catharina that it border~ the roads for miles, was dimorphic instead of trin1orphic. Although the ~istils. and stamens. vary greatly in ~en()'th, as was evident In some specnnens sent to me, y~t the plants can be divided into two sets, according to the lengths of these or?ans. A large proportion of the anthers are of a V: hi te colour and quite destitute of pollen; others which are pale yellow contain many bad with son1e good grains; and others aaain which are bright yellow have appare~tly sound p~ilen · but he has never succeeded in finding any fruit on 'this species. The stamens in s01ne .of the flowers are partially converted into petals. Fntz l\'liiller after readinO' my description, hereafter to be given, of the illegitimate offspring of various heter~stylecl species, suspects that these plants of o.xahs may be the variable and sterile offspring of a single fonn of some triinorphic species, perhaps accidentally introduced into the district, which has since been CHAP. IV. OXALIS, HOMOSTYLED SPECIES. 181 propagated asexually. It is probable that this kind of propagation would be much aided by there being no expenditure in the production of seed. Oxalis (Biophytum) sensitiva.-This plant is ranked by many botanists as a distinct genus. Mr. Thwaites sent me a number of flowers preserved in spirits from Cey Ion, and they are clear I y trimorphic. The style of the long-styled form is clothed with many scattered hairs, both simple and glandular; such hairs are much fewer on the style of the mid-styled, and quite absent from that of the short-sty led form ; so that this plant reseinbles in this respect 0. Valdiviana and Regnelli. Calling the length of the two lobes of the stigma of the long-styled fonn 100, that of the mid-styled is 141, and that of the short-styled 164. In all other cases, in which the stigma in this genus differs in size in the three forms, the difference is of a reversed nature, the stigma of the long .. styled being the largest, and that of the short-styled tlle smallest. The diameter of the pollen-grains from the longest stamens being represented by 100, those from the mid-length stamens are 91, and those from the shortest stamens 84 in diameter. This plant is remarkable, as we shall see in the last chapter of this volume, by producing long-styled, mid-styled, and short-sty led cleistogamic flowers. Homostyled Species of Oxalis.-Although the majority of the species in the large genus Oxalis seem to be trimorphic, some are homostyled, that is, exist under a single form ; for instance the common 0. aeeto .. sella, and according to Hildebrand two other widely distributed European species, 0. striata and eornimdata. Fritz Muller also infonns me that a similarly consti .. tuted species is found in St. Catharina, and that it is |