IMPROVEMENT OF STOCKS 349 



described by Sachs and other authors, but no one seems to have noted 

 that while Schacht's picture and description are true of many cottons 

 there are other species that manifest totally different conditions : namely, 

 those described by Strasburger, and also by Sachs, as present in Malva and 

 Althoea. 



2. Strasburger furnished, however, an admirable series of illustrations Stras- 

 of the pollen-grains of Malva crispa (' Lehrbuch der Bot.' 1894, p. 368) burger, 

 which were presumed apparently to exemplify a condition that prevailed 



in the MALVACE.E. The sculpturings (as they are sometimes called) of the 

 exine, shown by Strasburger as characteristic of Malva, closely resemble 

 those of O. arboreum and other species of Gossypium. (See Plate 52, 

 ff. 4 & 7 and 53, if. 15 & 18.) 



3. Sachs (' Text-book of Botany,' Vine's transl., 2nd ed., 1882, p. 555) Sachs, 

 gives an interesting review of the information then available. He remarks 



that the characteristic features of the outer wall of the grain often depend 

 on the number, position, and nature of the openings or perforations in 

 the outer wall. His drawing depicts pores or channels between the 

 surface warts. The illustration given manifests the condition seen in 

 Althaea rosea, but it is also present in some of the cottons, as, for example, 

 in O. barbadense (Plate 53, f. 11). Through the openings or rupturings of 

 the exine, the hernia-like protuberances of the intine emerge the pollen 

 tubes. 



4. Mr. M. Pakenham Edgeworth devoted many years to the study of Edge- 

 the pollen-grains of the chief groups and families of plants, and wrote a " wort "- 

 most useful little book on ' Pollen,' the second edition of which was 

 published in 1879. He does not seem, however, to have taken up any one 

 family and investigated all its species and cultivated forms (such as Mr. 

 Slater has even already accomplished with Gossypium), and accordingly 

 Edgeworth arrived at no very definite conclusions as to the value (if any) of 



the forms of grains as denoting genera, still less species. He figures, 

 describes, and gives the measurements, of some 438 different grains, and thus 

 affords many useful particulars regarding the subject collectively. 



In connection with VIOLACEJE, Edgeworth points out that a hybrid 

 between Viola tricolor and V. cornuta showed ' some of the characteristics 

 of both parents. This is very remarkable, as Mr. Worthington Smith 

 has pointed out that it is impossible to cross species which have different 

 pollens ; but this does not seem to be universally the case, at any rate. 

 No doubt the subject will be carefully examined by hybridists, to whom it is 

 most important.' I am not aware that this subject has been materially 

 advanced since Edgeworth penned these words, though numerous writers 

 have mentioned the discovery of more than one kind of grain in the anthers 

 of one and the same plant. 



5. Several instances of this might be mentioned, but one or two may 

 suffice in this connection. It has been observed that while the majority 

 of the forms of sweet peas have ' long pollen-grains,' one, the ' Emily 

 Henderson,' has usually ' round grams.' It has further been recorded that 

 when round-grained ' Henderson,' with pure white flowers, was crossed with 

 long-grained ' Henderson,' also with pure white flowers, the result was seed 

 which gave the old purple sweet pea (with chocolate-coloured standards and 

 blue purple wings), but no manifestation appeared of the white condition of 



