262 STTMMAEY OF CURKENT RESEARCHES RELATING TO 



A certain difference must be noted between the formation of the 

 embryo of Orchis maculata and that of Alisma Plantago, which is re- 

 garded as the type of monocotyledons. In the former case the 

 embryo, composed at the outset of three cells, is formed from two 

 superior cells, and partly from the inferior cell ; in the latter case it 

 is formed from the superior and partly from the middle cell. But in 

 the formation of the first longitudinal walls arranged in a cross, the 

 resemblance is complete. 



For rendering the embryo transparent, M. Monteverde employed 

 spirits of wine, alkali, and acetic acid. The youngest were placed in 

 a 10 per cent, alkaline solution, usually for not more than two days. 



Course of the Pollen-tube in Angiosperms.*— M. Detmar has 

 made a detailed examination of the structures by means of which the 

 jjassage of the pollen-tube into the ovary and into the ovule is 

 facilitated. The very large number of cases examined he divides 

 into six classes, advancing from the simpler to the more complicated. 



1. In Gymnosperms the contrivances which conduct the pollen- 

 tube to the corpuscula are very simple, the course being direct, and 

 usually very short. The pollen-grains fall directly on the nucellus, 

 the tissue of which, as far as the corpuscula, is very loose. In 

 Welwitschia the corpuscula develop into long tubes within the 

 nucellus, meeting the pollen-tubes. The Loranthaceas exhibit a very 

 simple structure in their conducting apparatus, analogous, but not 

 homologous, to that of Gymnosperms. In Viscum album there are 

 from two to four embryo-sacs, above which the nucellar tissue is also 

 very loose. In Loranthus bicolor the embryo-sacs meet the pollen- 

 tubes, like the corpuscula of Welivitschia. 



2. The course of the pollen-tube in Angiosperms depends, in the 

 first place, on the position of the micropyle. The most favourable 

 structure is when the micropyle lies immediately beneath the base of 

 the style, of which Polygonum divaricatum furnishes a good example. 

 The conducting tissue of the three styles projects in the form of a cone 

 into almost immediate contact with the apex of the ovule ; as is also 

 the case in Daphne Mezereum. In the Compositfe (e. g. Senecio Doria) 

 the conducting tissue of the style consists of two closely adjacent lines, 

 which separate when they reach the cavity of the ovary, passing down 

 the two sides, and meeting again beneath the basilar anatropous ovule. 

 They consist of strongly mucilaginous cells, which are often isolated 

 on transverse section. The micropyle is entirely filled with mucilage. 

 In Plumbaginese the long coiled funiculus brings the micropyle of the 

 anatropous ovule immediately beneath the base of the styles. A cone 

 of conducting tissue descends from the base of the five united styles 

 nearly to the ovule. The Chenopodiaceae, with their campylotropous 

 ovules, display a similar contrivance. 



3. The process is not so simple where the micropyle does not lie 

 immediately beneath the base of the style. In Ricinus the ovary is 

 trilocular, each loculus containing a single anatropous ovule. The 

 conducting canal of the style branches within the ovary into three ; 



Jenaische Zeitschr. Naturwiss., xiv. (1S80) pp. 530-66. 



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