PHANEROGAM! A : FLOWERS. 407 



them, ffelianthemum, (fig. 251.), I pledge myself to lay bare the tube 

 from the stigma to the seed-bud in a few minutes, which plants I select 

 annually for demonstration in my Lectures, in others I have often dis- 

 sected a week, and even a fortnight, from early till late, before I once 

 succeeded in perceiving, with full certainty, the whole course of the 

 pollen-tube. Nay, sometimes my observations have remained quite im- 

 perfect in one year, and only been completed by resuming them in the 

 following. I remark this here, because I find that many imagine the 

 matter to be very easy, and when they have not succeeded in the first 

 attempt, think at once their negative observation has sufficient value to 

 set aside the assertion of others, while it only bears testimony to their 

 want of skill or impatience, and this indeed most decidedly.* The best 

 method of proceeding is to cut from the axis of the entire pistil, with a 

 broad, sharp knife (I always use a razor), a lamella, not too delicate, so 

 that the section may contain part of the stigma and the conducting tissue, 

 as perfect as possible, down to the seed-bud. This section must then be 

 brought under the simple microscope, and the whole of the pollen-tubes 

 present separated with the needle from the cellular tissue on which they 

 lie, beginning at the stigma and proceeding to the seed-buds ; then the 

 funiculus of these is to be cut away from the spermophore, taking care 

 not to cut through the pollen-tubes at the same time, and the attempt 

 made to separate the single tubes from each other until you are 

 guided by one of these to the micropyle. One must frequently be con- 

 tent to perform the operation piecemeal, by examining, one after ano- 

 ther, as long pieces as possible of the conducting tissue, from the stigma 

 to the seed-buds, and thus to make sure of the complete descent of the 

 pollen-tube. The search for and tracing of the tubes is most facilitated, 

 especially in the Dic/wgamece, MonocistcR^ and Diocistce, by applying the 

 pollen of recently-burst anthers to a perfectly developed stigma, and 

 then examining at different periods. The time required to complete the 

 process of growth varies very much : in the style of Cereus grandiflorus, 

 nine inches long, the end of the pollen-tube reaches the seed-bud in a 

 few hours ; in that of Colchicum autumnale, of thirteen inches long, in 

 about twelve hours ; in others it is often weeks before it has traversed 

 the very short distance. Besides, the pollen-granules, which are also 

 often carried to the stigma at different times, do not all grow down 

 simultaneously. Finally, the persistence of the upper end, which still 

 sticks or did stick in the pollen-granule, varies much ; while in some 

 plants the pollen -tube remains perceptible in its whole length for weeks, 

 in others it dies away above almost as fast as it grows below. In plants 

 of which the stigmatic fluid hardens into a kind of membrane, the por- 

 tion of the tube between this membrane and the pollen-granule often 

 remains visible for a long time, while the portion from the membrane to 



* This difficulty in the investigation, which only occurs in certain cases, is by 

 no means the reason why in this, the most important of all studies, from 1823, when 

 the question was raised by Amici's discoveries, to 1842, only five, say five, men can be 

 named who have contributed to its progress : but the usual indifference of most botanists 

 to all deeper and really scientific investigations. How essentially the answering of 

 the whole question is thereby modified, whether the stigma is clothed by a dense, 

 structureless membrane, is evident. Brongniart had asserted the existence of such a 

 membrane in Nympha-a, Hibiscus, and Mirabilis, in 1827: in 1837 Link said, "Accord- 

 ing to Brongniart, it is so." Therefore, during ten years, he had not thought it worth 

 the trouble once to look into these plants, which are everywhere to be found, to confirm 

 or refute Brongniart's opinion. Is anything like tin's really heard of in any other branch 

 of natural science ? 



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