Seedling Anatomy of Ranales, Rhoeadales, and 
Rosales . 1 
BY 
E. N. THOMAS. 
Reader in Botany in the University of London. 
With Plates L and LI and forty-three Figures in the Text. 
T HE present century has seen a very vigorous output of work dealing 
with the anatomical features of the so-called transition between root 
and shoot structure in Phanerogams. This has, to a large extent, only 
been possible since the everyday use of the microtome has rendered serial 
examination of the youngest and slenderest seedlings a matter of ease. 
Even the most skilful manipulator of hand sections must fail signally to 
obtain much insight into the anatomical relationships of nine-tenths of the 
forms during their most illuminating stages. 
In comparison with the work of the earlier anatomists in this field 
(Van Tieghem, 2 Gerard, 3 Dangeard, 4 &c.) the investigators of the 
twentieth century have all felt it incumbent upon them to deal with very 
young seedlings, but some have not been so rigorous as others in this 
respect, and I wish to associate myself with M. Chauveaud in emphasizing 
the extreme importance of this precaution. Primary structures are not 
merely obscured at a later date, but may be obliterated. Chauveaud has 
laid great stress upon this phenomenon and demonstrated it in many 
forms, notably in Mercurialis annua? while I discovered it to be the case 
so early as 1902 in Cleome sesquiorgialis , and subsequently in many other 
species, including the common Wallflower. 6 Serial sections running through 
cotyledons, hypocotyl, and primary root of seedlings at different ages prove 
conclusively the extraordinary changes which take place with age, leading 
to the disappearance of groups of protoxylem elements. This point has 
1 Thesis approved for the Degree of Doctor of Science in the University of London. 
2 Van Tieghem, Ph. : Traite de Botanique. (Paris, 1891.) 
3 Gerard, R. : Recherches sur le passage de la racine a la tige. Ann. Sci. Nat., Bot., s^r. vi, 
t. xi, 1881. 
4 Dangeard, P. : Recherches sur le mode d’union de la tige et de la racine chez les Dicotyle- 
dones. Le Botaniste, ser. i, 1889. 
5 Chauveaud, G. : L’appareil conducteur des plantes vasculaires et les phases principales de son 
evolution. Ann. Sci. Nat., Bot, ser. ix, t. xiii, 1911. 
6 Cf. account of transition in Wallflower in 7th and 8th eds. of Scott’s Structural Botany— « 
Flowering Plants. 
Annals of Botany, Vot XXVIII. No. CXII. October, 1914. 
