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GARDENERS' CHRONlCLh 



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I A Lesson on Plant Physiology and the Plant in | 



I Relation to Its Environment I 



1 Eeing One of a Series of Lessons c-f a Home Study Course on Gardeninij. Appearing Regularly in The Gardeners' Chronicle 1 



I Ur.der the Direction of ARTHUR SMITH | 



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Wii callfd attention last month to plant cells, and in mention- 

 ing that the starting point of a multicellular plant's 

 separate existence that reproduces itself from seed, is the 

 fertihzing of the ovule in the ovary (fruit) situate at the bottom 

 of the pistil, by the pollen produced by the stamen, we might 

 have added that this is practically the union or fusion of the 

 female cell in the ovary with the male cell of the pollen. 



Not only are plants, as we previously stated, so many chemical 

 laboratories ensaged in the manufacture of all kinds of chemical 

 bodies, but each living cell is itself an individual laboratory, and 

 is the seat of all those complex chemical and physical changes, 

 and energy transformations, which are the cause of a plant's 

 growth and development. 



In unicellular plants the cell is a complete and distinct unit, 

 acting independently; in a multicellular plant, while respondhig 

 also as a complete unit, a cell works in co-operation or in unison 

 with other cells associated together. There is not only co-opera- 

 tion among cells, but also organized division of labor, and this 

 has become developed to such an extent that certain cells have 

 special activities and each cell, or co-operative group of cells, 

 carry on their particular part connected with the growth and 

 development of the plant and with all the functional activities 

 associated therewith, side by side with others whose occupation is 

 something entirely distinct, and this under conditions which show 

 that there is something more than physical force behind their 

 activities. Marked examples of this are seen when the formation 

 of hard seed-cases (testa) synchronizes with the development of 

 a watery pulp, like, for examples, the fruits of the peach and the 

 melon. Also, in connection with plants having woody stems, we 

 see the cambium consisting of a continuous layer of growing 

 cells full of protoplasm, and the formation of the wood-ring or 

 seasonal growth on the inner and that of the bar'.- on the outer 

 sides of the cambium. 



Fertilization results, we repeat, in the union and fusion of two, 

 single, sex-cells (gametic), one being derived from the pollen 

 grain and the other from the ovule. These have been previously 

 differentiated by a series of special developments, and wheti de- 

 rived from different plants, or from different species or varieties 

 of plants, the characters of two individuals are fused and two, 

 more or less extensive, lines of ancestry are brought together 

 into one cell, the fertilized egg, which will develop into the 

 embryo of the seed. 



Ample provision against the death of any race of plants is 

 made in the act of reproduction. Although reproduction appears 

 to be useless to the individual and even entails upon it not only 

 serious losses of matter and energy, and in annual plants espe- 

 cially, death itself, yet to this function every part of the plant 

 directly or indirectly contributes. The reproductive cells are 

 carefully prepared, are provided with a stock of food sufficient 

 for the earliest stages of development, and are endowed with the 

 peculiar powers and limitations of each species which influence 

 their life-history at every step, and are by them transmitted in 

 turn to their descendants. They are living portions of the parents 

 detached for reproductive purposes and they contain a share of 

 cell protoplasm directly descended from the original protoplasm 

 from which the parent came. In short, we are caused to believe 

 that reproduction is the supreme function of the plant. 



It is a wonderful fact that living things have this power to de- 

 tach from themselves portions or fragments of their own bodies 

 endowed with fresh powers of growth and development and 

 capable of running through the same cycle as the parent. There 

 is therefore an unbroken continuity of the germ-plasm from one 

 generation to another that forms the physical basis of inheritance, 

 and upon which the integrity of the species depends. Living 

 things never arise save through this process, or through a process 

 which practically amounts to the same thing. In other words, 

 every bit of existing protoplasm is the last link in an unbroken 

 chain that extends backward in the past to the first origin of 

 life, or of the life of the particular race to which it belongs. 

 Wliatever theory we may hold as to the origin of life — and no 

 scicntilic statement of this origin is possible — the fact that today 

 spontaneous generation is non-existent has been so w'ell proven 

 as to be beyond discussion. 



While as a general rule the embryo of a seed cannot exist 



without the fertilized egg-cell being previously brought into 

 existence, still cases aie not uncommon where seed is produced 

 capable of giving rise to plants without fecundation. This phe- 

 nomenon is called parthenogenesis and is said to be characteristic 

 of some forms of dandelion, hawkweed, yarrow, etc. 



Reproduction without immediate fertilization is a well estab- 

 lished occurrence during part of the lives of certain insects and 

 other lower animals. Aphids, for example, at some periods pro- 

 duce by v\'hat is known as "budding off", full-grown, sexless in- 

 dividuals, without fecundation. A more generally known case, 

 and also perhaps the most marked is in connection with the hive 

 bee. Without fertilization the queen bee will produce fertile 

 eggs which, however, only give rise to drones. After fertilization 

 eggs giving rise to worker or neuter bees only are produced, and 

 we believe that in no case is a queen bee naturally produced 

 from an egg. Queens are brought into existence artificially, we 

 may in a sense say, by the neuter bees commencing to feed larvae 

 immediately after the eggs hatch with a special kind of prepared 

 food and continuing this feeding throughout the larval stage and 

 at the same time giving these larvje a special environment. 



While parthenogenesis in flowering plants is not of great prac- 

 tical importance, it is mentioned as being an interesting e.xcep- 

 tion to the .general rule, and it may be said to be the invariable 

 method of reproduction among the majority of flowerless plants. 



.\mong flowering plants, however, as also among the insects 

 mentioned this method is not continuous, but alternates with 

 fecundation, and is sometimes described under alternations of 

 generation. 



In the embryo, the inherent characteristics and possibilities for 

 development possessed by its parents, and to a minor degree any 

 variations acquired by either or both of them, are fixed, and 

 every plant grown from seed and spores has a certain definite 

 and changeless character which was inherent in the embryo from 

 which it sprung, which character is made up of different ten- 

 dencies, potentialities and limitations of development, inherited 

 in different and varying degrees from each of its ancestors for an 

 indefinite number of generations, plus more or less influence 

 exerted by climatic and other environmental conditions affecting 

 the development of the seed-producing plant. Invariably the in- 

 fluence of the immediate parents is the predominating one, but 

 sometimes a transmitted characteristic or characteristics of an 

 ancestor, which have remained dormant or repressed for many 

 generations, appear in such a way as to materially change for 

 good or evil the character of the plant. 



It is this general faculty for transmitting the characters of 

 its parents possessed by the embryo of the seed which renders 

 possible the improvement of plants by selection and hybridization, 

 and also the maintaining an improved variety in its higher state. 



It must be borne in mind that practically all our garden plants 

 raised from seed have come from a wild type and in many cases 

 few would recognize that type as being botanically the same as 

 its garden representative. How strong is the pull of ancestral 

 germ-plasm is shown by the tendency of improved varieties to 

 revert back to the original wild type. While this tendency 

 works more quickly in some species than in others, it is only 

 through continual re-selection and elimination (roguing) by 

 seed-growers that the standard of improvement is kept up and 

 increased. 



What are known as "stock-seeds" are grown by seedsmen upon 

 their own farms under rigid supervision so that each variety 

 may be of the highest standard of purity and excellence. These 

 stock-seeds are subsequently given out to men who make a busi- 

 ness of growing seeds under contract and the seedsman giving 

 out the stock receives the whole of the produce. There are 

 probably not many more, even if as many, than a hundred seeds- 

 men in the whole of the United States who produce their own 

 stock-seeds. The production, as apart from mere selling, of 

 really high-class seeds is very expensive and requires a consider- 

 able outlay of capital. Seeds of this character must be sold at 

 a higher price than those raised at a much less expense, but 

 they are always cheaper than those of inferior quality, whatever 

 price is paid. Seed selection is of the greatest importance and 

 no gardener can really afford to be indifferent as to the quality 

 of the seed he sows. It is not enough that the seed be plump 

 and of a high standard of germination; it should be from care- 



