268 



NA TURE 



\July 19, 1883 



a few remain broad, and finally acquire a triangular form 

 with sharply pointed corners. 



Meanwhile, the colour passes through intermediate 

 dirty shades from green to brick-red ; and, some time 

 before the flower bud opens the ultimate shape and colour 

 are attained, and the bodies are now called chronto- 

 plastidia. Many similar instances have established the 

 connection between the three kinds of plastidia* e.g. 

 petals of Scnccio, Bellis, Tropaolum, fruits of Sorbus, 

 Rosa, Lonicera, &c. 



The primitive plastidia are universally present in the 

 meristems of the higher plants, and have now been found 

 in so many seeds and embryos, that Schimper suggests 

 that they no doubt exist in the embryc-sac and oosphere 

 from the first. All the chloroplasts of the plumule and 

 stem-axis, &c, arise by division of the plastidia in the 

 punctum vegetationis of the young stem ; these may be 

 green from a very early stage, or acquire their green 

 colour later, or remain colourless (leukoplasts). In cases 

 where the leukoplasts form large starch grains, we have 

 the Starkebildner discovered by Schimper in 1880 ; all 

 the kinds of plastidia, however, may be fouid in connec- 

 tion with starch grains, which often become resorbed 

 later. 



In the same way, all the chloroplasts, leukoplasts, and 

 chromoplasts of the roots arise by division and differentia- 

 tion of the few primitive plastidia in the punctum vegeta- 

 tions of the radicle. 



Since chloroplasts or leukoplasts are found at a very 

 early age in the embryos of Crucifers, Lcguminosor, 

 Geraniacece, and many others, Schimper considers it 

 probable that they arise from primitive plastidia in 

 the oosphere. Chloroplasts and leukoplasts (as starch- 

 forming corpuscles) are visible in the embryo of Linum 

 austriacum when it consists of eight cells only, and 

 the minute starch-grains observed in the embryo sac 

 and oosphere of that plant are no doubt contained in 

 leukoplasts — which become green afterwards and are 

 then visible. Schimper finds that the primitive plas- 

 tidia may remain colourless as leukoplasts — which, if 

 they form starch grains, are the Starkebildner of his 

 earlier papers — or may become chloroplasts, as is usual 

 (but by no means universal) in cells exposed to light, 

 which remain green, or pass over into chromoplasts (most 

 flowers and fruits). Nevertheless, the order of change is 

 not fixed, and no sharp lines can be drawn — thus, a 

 leukoplast may become green, and function as a chloro- 

 plast for a time, and finally lose its colour again, and 

 become a leukoplast. 



The Characeoz seem to be the earliest plants in which 

 all three forms of these bodies occur ; the apical cells 

 containing leukoplasts, and the antheridia red chromo- 

 plasts. Schimper suggests that if the oosphere is proved 

 to contain already formed plastidia, it will support the 

 view that the higher green plants owe their origin to 

 symbiosis of green and colourless organisms. The author 

 enters into no particulars, however, concerning this hypo- 

 thesis, which appears by no means obvious in the light 

 of other considerations. 



1 A. Meyer terms the bodies ana-plasts (=leucoplastidia), auto-plasts 

 (= chloroph^tidia). and chromo-plasts (= chromoplastidia) respectively. He 

 uses tin: Reneric term trophoplasts to embrace all collectively. We may call 

 them leuko-, chloro-, and chromo-plasts, since these names imply no 

 functional peculiarities. 



The following may be selected as further illustrations 

 of Schimper's work : — 



1. Leucoplas/s arise from colourless plastidia (roots, 

 &c.) or, more rarely, from chloroplasts {e.g. fruit of 

 Symphoricarpus). They may become green chloroplasts 

 (many embryos), or function as Starkebildner (e.g. 

 deeply-situated cells), or remain apparently without 

 function (e.g. epidermis cells). In many flowers they 

 become chromoplasts. 



2. Chloroplasts (i.e. chlorophyll corpuscles) arise from 

 the growth and division of primitive plastidia which are 

 already green, or by the development of green colouring- 

 matter in leukoplasts exposed to light. They often 

 become chromoplasts later. 



3. Chromoplasts. — All shades occur between pure car- 

 mine-red and greenish-yellow — never blue — the earlier 

 statements being based on errors of observation. 1 



The development of the colouring matter is frequently 

 attended by a disappearance of the starch grains on or in 

 the leukoplast or chloroplast from which the chromoplast 

 arises. As sometimes occurs with other bodies, the 

 spindles, needles, and tablets produced as the ultimate 

 forms of the chromoplasts appear to proceed from a pro- 

 cess of crystallisation of certain of the proteid contents 

 of the chromoplast from a formless matrix of living pro- 

 toplasm. In these cases the pigmented tablets, needles, 

 rods, &c.j must be regarded as crystalloids. More rarely 

 the proteids of the leukoplasts and chromoplasts separate 

 in the same crystalline form. 



Schimper distinguishes three types of chromoplasts : — 



1. The spherical type, found in the arillus of Taxus, 

 fruit of Solatium, &c. 



2. Two or more pointed needles, tablets, &c, of 

 Hemerocallis, Lilium, Tropaolum, and other flowers. In 

 the fruits of Rosa, Lonicera, &c., both these types occur 

 together. 



3. In this type the chromoplasts are rod-shaped — e.g. 

 flowers of Tulipa, root of Daucus, &c. 



No relations can be discovered between the form, &c, 

 of any of these bodies and the natural groups in which 

 they occur. H. Marshall Ward 



OUR BOOK SHELF 



The Forests of England and the Management of them 

 in Bygone Times. By John Croumbie Brown, LL.D. 

 (Edinburgh : Oliver and Boyd, 1883.) 



French Forest Ordinance of 1669, with Historical Sketch 

 of Previous Treatment of Forests in France. Com- 

 piled and Translated by John Croumbie Brown, LL.D. 

 (Edinburgh : Oliver and Boyd, 1883.) 



These two little books, published almost simultaneously 

 but in the order in which their titles are given above, have 

 been written, as Dr. Brown tells us, "nsa small contribu- 

 tion to the literature of Britain on subjects pertaining to 

 forest science." The author has shown in previous 

 writings on kindred subjects the scarcity of English 

 literature on forestry as compared with that of France 

 and Germany, and he again draws attention to this fact 

 by copious extracts in " The Forests of England " from a 

 little work of his on " The Schools 'of Forestry in 

 Europe," published in 1877. 



The forests of England, exclusive of their practical 

 utility, have played a not unimportant part in the history 



1 Schimper points out how easily such bodies as these are altered by pro- 

 cesses hurtful to the cell : they must be observed in perfectly fresh, uncut, 

 and uninjured cells. 



