710 



HORTICULTURE 



June 2, 1906 



grains (somewhat larger in propor- 

 tion than they ought to he) on the 

 stigma, the tubes penetrating the 

 loose tissue, and one that has already 

 crept down the wall of the ovary and 

 up to an ovule. That the tube should 

 go directly to the pore of the ovule 

 seems like an exhibition of intelli- 

 gence until we find by experiment that 

 such tubes in cultures may be directed 

 in their growth by emanations of ma- 

 lic and other organic acids. We sup- 

 pose therefore that the ovule emits 

 some such active substance which ex- 



Fig. 5. Flowers of the willow. From 10O 

 to 200 flowers like these make up a cat- 

 kin: A. staminate flower consisting of 

 2 stamens (s t); B, pistillate flower, con- 

 sisting of one pistil, the stigma at s; 

 C, pistil opened, showing ovules (ov); 

 g, honey gland; enlarged. 



ercises a directive influence over the 

 tube's course. As in the spruce and 

 all other flowering plants a small fer- 

 tilizing body, a nucleus, is produced 

 by the pollen grain for the fertiliza- 

 tion of the so-called egg nucleus in 

 the embryo-sac. After the arrival of 

 the tube at the sac and the entrance 

 of the fertilizing nucleus, fusion takes 

 place and a new willow has begun to 

 have its being. 



My chief excuse for recounting what 

 must be known, in its main outlines 

 at least, to many readers is the illus- 

 trative value of the drawings, which 

 naturally require a commentary. I 

 am tempted to add some . remarks on 

 the history of the theory of sexuality 

 in plants — for it is plain that repro- 

 duction in plants is like that of ani- 

 mals in the central fact of the uniting 

 of two minute, inheritance-bearing 

 bodies as the initial step in the for- 

 mation of a new individual, and that 

 plants therefore are truly possessed of 

 two sexes. The history of opinion, 

 beginning in surmise, and passing 

 through the stages of observation, ex- 

 periment and minute research to our 

 present full knowledge, is interesting 

 in the extreme: and even the mere 

 suggestive sketch possible here may 

 be worth while. We of today speak 

 of the phenomena of pollination, fer- 

 tilization, embryo and seed-formation 

 so easily and assuredly, as things of 

 common information, that we do not 

 easily grasp the difficulties which ear- 

 ly naturalists had to overcome in win- 

 ning true ideas of the matter. Some 

 of the views of old writers are fantas- 

 tical and amusing, and those of some 

 investigators not so very old now ap- 

 pear curiously mistaken. To us who 

 are in the midst of the swift current 



of discovery by experiment the most 

 interesting aspect of the whole history 

 is perhaps the delay of many centuries 

 before any one of the numerous stu- 

 dents of plants who touched upon the 

 subject of reproduction, made the 

 smallest attempt at experimental 

 study. 



Some Greek and Roman writers 

 speak of plants as male and female: 

 but their notions were of the most 

 general and unsubstantial sort. 

 "Male" and "female" as applied to 

 plants often meant nothing more than 

 sterile and fertile. It was indeed 

 observed that the seed plant in 

 some cases becomes productive 

 only when a pollen plant is near; 

 but Aristotle, the chief natural 

 philosopher of antiquity, though 

 truly gifted with wonderful in- 

 sight in many things, classed this 

 fertilizing effect among pheno- 

 mena of nutrition; nor did he 

 make any attempt to find out by 

 experiment whether pollen is 

 universally needed for seed-set- 

 ting. 



Coming down to recent times, 

 even subsequent to the beginnings 

 of modern science (which we 

 -OV count as commencing with Lord 

 Bacon) we find the first of Eng- 

 lishmen to study plants atten- 

 tively with the microscope, 

 Nehemiah Grew, speaking thus of 

 the offices of stamens and peri- 

 auth: "And First, it seems, 

 That the Attire [stamens] serves 

 to discharge some redundant Part 

 of the Sap, as a Work prepara- 

 tory to the Generation of the 

 Seed. In particular, that as the Folia- 

 ture [petals and sepals] serveth to 

 carry off the Volatile Saline Sulphur: 

 So the Attire, to minorate and adjust 

 the Aereal; to the end. the Seed may 

 become the more Oyly, and its Prin- 

 ciples, the better fixed. And therefore 

 the Foliature generally hath a much 

 stronger Odour, than the Attire: be- 

 cause the Saline Sulphur is stronger, 

 than an Aerial, which is too subtile 

 to affect the Sense. Hence also it is, 

 that the Colour of the Parts of the At- 

 tire, is usually White, or Yellow, 

 never Red: the former, depending up- 

 on a greater participation of Aer; the 

 latter, of Sulphur." Further on he 

 adds: "And the Globulets [pollen 

 grains] and other small Particles up 

 on the Blade are as the Vegetable 

 Sperme. Which falls down upon the 

 Seed-Case or Womb, and so touches 

 it with a Proliflck Virtue." All we get 

 from Grew is the conjecture that the 

 stamens produce the male element in 

 fertilization. 



The doctrine of sexuality in plants 

 was really founded by Camerarius, 

 the ingenious and lucid-minded profes- 

 sor of botany in the University of Tu- 

 bingen, in Germany, about 1690. He 

 experimented with various plants and 

 proved that in general pollen is neces- 

 sary for fertility. For example, to 

 quote his words: "When I removed 

 the male flowers of Ricinus before the 

 anthers had expanded, and prevented 

 the growth of the younger ones but 

 preserved the ovaries that were al- 

 ready formed, I never obtained perfect 

 seeds, but observed empty vessels, 

 which fell finally to the ground ex- 

 hausted and dried up. In like manner 

 I carefully cut off the stigmas of Mais 

 that were already dependent, in con- 

 sequence of which the two ears re- 



mained entirely without seeds, though 

 the number of abortive husks (vesi- 

 cularum) was very great". He gave 

 what was up to his time the best ac- 

 count of the structure of the flower 

 and its functions. Some of his experi- 

 ments were failures, however, for 

 some plants do set seed without pol- 

 len — for reasons which we now know. 

 Consequently his conclusion, that 

 plants possess true sex characters, was 



Fig. 6. A, pollen grain considerably mag- 

 nified; B, lengthwise section of the fe- 

 male flower, showing the course of the 

 pollen tube and 3 ovules, one split length- 

 wise; g, grains on the stigma; pt, pollen 

 tube; es, embryo sac. 



strongly opposed by many botanists, 

 and disputes upon the fact of sexual- 

 ity continued for the better part of a 

 century. 



Koelreuther's famous work in hybri- 

 dizing settled the fact. It will doubt- 

 less surprise some who are familiar 

 with the practical results of crossing 

 species to learn that the first service 

 of hybridization was to theoretical 

 science. When Koelreuther about 1760 

 published his investigation he showed 

 that the hybrid mingles the characters 

 of the parents; and from this result 

 he drew the important conclusion that 

 the offspring inherits substance from 

 both paternal and maternal parent: a 

 demonstration and conclusion which 

 could not have been had from two 

 plants of the same species. 



Pollen tubes were first seen by 

 Amici, the Italian optician, accident- 

 ally, when for another purpose he was 

 examining the stigma of a Portulaca, 

 in 1S23. He observed, in fact, the 

 actual germination of the grain. 

 Seven years later he followed the pol- 

 len tubes into the ovary and observed 

 that one tube finds its way into the 

 microphyle of each ovule. Soon after- 

 wards Schleiden took up the further 

 development, and believed that he saw 

 the end of the tube pushed into the 

 embryo sac and there become the re- 

 ceptacle in which the embryo is 

 formed. Schleiden and his followers 

 stoutly maintained the mistake until 

 Amici himself, in 1846, proved the ex- 

 istence of a body in the embryo-sac, 

 namely the egg-cell, which is excited 

 by the influence of the pollen tube to 

 further development and becomes the 

 embryo. The exact nature of this in- 



